Jump to content


Chasing the Tail of pH

  • Please log in to reply
1 reply to this topic

#1 Simon Garratt

Simon Garratt

    Trigger Fish

  • Members
  • 644 posts

Posted 21 July 2008 - 07:32 AM

Chasing the tail of pH

In this article, I will attempt to cover one of the most frequently aggravating and perplexing subjects we come across in reefkeeping, and hopefully it will put a few wrongs to rest. If nothing else it give you a few ideas that you may wish to try out in an effort to solve any recurring issues you have with your pH then its served a valuable purpose. pH in its entirety is a very complex subject where reef tanks are concerned so I’ve tried as much as possible to avoid any complex equations and chemistry, Alas though, there are some inescapable links between what goes on at a chemical level, your stock and your hardware so please bare with me. Hopefully I’ve put things across in a logical manner… So without further ado…

What is pH and pH drift ?

The pH scale as we know it represents a logarithmic translation of the differences in hydrogen ion concentration in a given aqueous solution (in our case sea water). Too complicated ? Ok, so to put it another way. We have a scale of 1 to 14 that represents whether a solution is acidic or alkaline in nature, with 1 representing the most acidic, 14 representing the most alkaline, and 7 representing a neutral level, i.e. pure water. The key to understanding the pH scale is in realising that it is a logarithmic scale i.e. a pH of 5.0 is 10x more acidic than a pH of 6.0 and a pH of 8.0 is 10x more alkaline than a pH of 7.0. as we move the margin further, the difference becomes cumulatively greater i.e. a pH of 4.0 is 100x (10x10) more acidic than a pH of 6.0, and so on and so forth.

Posted Image

Greedy fish place a big load on your pH. Too many, and your system struggles to deal with the waste generated.

In relation to what we see in our aquariums, we are usually hovering between the 7.7 to 8.5 mark with 8.5 being 70x more alkaline than 7.7. As a general rule we use NSW (natural sea water) as a basis for our needs, with a guide parameter of 8.3 to 8.4 considered as an ideal. The drift we commonly encounter over the course of either 24 hrs or long term, represents the shift in hydrogen ion concentration within our water. Although in its entirety the chemistry involved can be quite complex, the largest factors we commonly encounter, are directly attributed to the balance between o2 / co2 concentrations, and the waters ability to buffer against pH suppression through increasing Co2 levels and lowered o2 concentration. So what is a good pH and what’s a bad pH? The general consensus among experts is that we should try and avoid running pH outside the comfortable extremes of 7.7 to 8.5 in a reef aquarium, with the higher end being considered the more ideal. What is commonly missed out and frequently witnessed by those keeping more sensitive species such as SPS corals, is that the overall reading seems to be less of a concern than the overall stability or drift. Many now attribute more stable growth, better colouration, and lower mortality with SPS corals under stable conditions with minimal 24 hr drift (below 0.10) than a higher pH but with a wider drift. So it’s up to the individual to decide on which side of the fence they fall and where they want to focus attention. In effect though, the results of the following, will hopefully herald results in both quarters, i.e. a higher overall pH reading, and a more stable 24hr drift.

So, to get control of pH issues we first need to know what the major factors are affecting it within any individual system. By and large we can break these factors down into five distinct areas.

Firstly we have the largest factor of all. Bio-load. All organisms within the reef aquarium require oxygen to a greater or lesser degree from fish to bacteria. Even algae which are known for their ability to utilise Co2 and give off o2 during the lit period, switch to using o2 at night, and give off Co2 if not lit, hence the common reason for reverse lighting refugium’s in an effort to offset the 02 demand going on in the tank and stabilise day/night pH drift..
Bioload is important, as it links two key processes within the aquarium. Namely waste generation and waste breakdown. When we feed our fish or corals, a percentage is utilised for biological processes and growth ‘both of which require o2’. The rest is expelled as waste which feeds smaller and smaller organisms until we get to the final stage of bacterial breakdown to nitrate. In effect, each and every gram of food we feed, may take a multitude of paths before ending its journey. Each one of these paths steals from the 02 reserves of the system affecting the balance between 02 and Co2 causing a drop in overall pH. The more we feed, the greater this effect, as bacterial populations grow to take advantage of the larger nutrient reserves.

Posted Image Posted Image

Many consider pH stability crucial to success with SPS corals

Secondly, we have gaseous exchange. The air/ water interface, is a focal point where C02 escapes and 02 enters. Too smooth with little or no surface agitation, and gas exchange is restricted, so ideally we should have a very active surface layer to break up surface tension and allow gases to pass in both directions freely. Protein skimmers can also play an integral roll in this process as well. Delivering large volumes of air through the reaction chamber. This helps drive off excess Co2.as it is generated by the organisms present in the system. The more powerful the skimmer, the greater this beneficial effect. In fact, even weirs can play a roll, where the rushing air/water mix helps in the same manner the skimmer did.

Next we have the chemistry of the water itself, and how the various concentrations of elements affect how pH responds to these changes in 02 or Co2 levels. So without getting overly complicated, there are three main components to sea water that are linked in such a manner that they have a direct influence on the pH drift we encounter over any 24 hour period. Namely, Magnesium (Mg), Calcium (Ca) and Alkalinity (DkH / Meq/l). At first glance we may think that Magnesium has little to do with this relationship, but this couldn’t be further from the truth. At levels below NSW concentrations of around 1350ppm, we see an increasing loss of ability to maintain both Ca levels and Alkalinity regardless of the methods used to maintain or boost them. This is crucial to our goal, because Alkalinity ‘is’ directly linked to pH fluctuation. As levels drop below NSW levels of around 8.0 – 8.5 dkH, we see an ever increasing swing between our daytime high pH reading, and our lowest pH reading at the end of the unlit period. pH swing is important, because most marine organisms are extremely sensitive to pH changes. Many SPS and soft corals as well as crustaceans can suffer quite badly from excessive and repetitive daily changes. Keeping these three main chemical constituents at NSW levels of around 1350ppm Mg, 420ppm Ca and 8.0 DkH will minimise pH swings to more natural levels. Increasing dkH into the 10-12 dkH bracket has been seen to further stabilise pH drift, however the full consequences of excessively elevated dkH are still not fully understood beyond the possibility of brittle skeletal formation in some SPS. Even then it is recommended that Ca and Mg are brought up to balanced levels with this higher reading. A common mistake made by people trying to raise pH is to use pH buffer (usually Sodium bicarbonate) It should be noted that pH buffers derived of Sodium Bicarbonate will not ‘raise’ pH, even though a minor increase may be noticed for the first few hours after dosing. What Sodium bicarb does do, is to increase the dkH level, thereby buffering the pH against suppression below its normal and existing position. In effect, all buffers do, is bolster up the ‘lowest’ reading that’s encountered at the end of the unlit period. They won’t ‘raise’ the overall pH value to any degree. Whilst this may seem beneficial, the long term addition of these buffers will see a gradual increase in the number of sodium ions in the water, and a gradually increasing imbalance between Alkalinity, calcium, and Magnesium, so regular testing is essential where these parameters are concerned. If you affect one, you have to consider the others.

Next we have system maturity. Most systems when new will go through various stages of maturation and settling as bacterial and algal populations become established. In many cases we will see various blooms occurring during the first few months. These blooms will have an affect on the systems pH and should be expected. This is one reason that we should always stock new systems slowly to avoid putting extra pressure on the systems ability to stay stable, accepting that any animals we place in this environment, will have to put up with these changes as everything settles down. Equally, it is not unusual with new substrates to find some initial demand placed upon our Alkalinity, Magnesium and Calcium reserves as they are drawn from solution to bind to these surfaces and balance out the chemical differences between the water and the media itself. In these initial phases we may need to monitor these levels and boost accordingly through manual supplementation until everything has settled. This can commonly take a few months from the initial start up, during which time we will see initially wide swings in day / night time pH, settling over time to more consistent and stable readings as bacterial and algal populations even out, and chemistry has settled. As such we should avoid panicking unduly about pH stability in the early stages, and avoid chucking chemicals at the situation until we know whether we actually have a long term issue or not. Sometimes its just better to ride it out for the first few months, being sensible with our stocking regime and wait to see what happens a few months down the line.


Simon Garratt O.C.R.D

#2 Simon Garratt

Simon Garratt

    Trigger Fish

  • Members
  • 644 posts

Posted 21 July 2008 - 07:39 AM

Following on:

Finally, we have dosing regimes. When we run equipment like Calcium reactors or Kalkstirrer’s we are inputting solutions that are at two opposite ends of the pH scale compared to our aquarium water. With Kalkwasser having a pH of around 12.0 and Calcium reactors having an effluent of around 6.5 pH, It will come as no surprise that we should monitor the dosing of these two solutions quite stringently. Running a calcium reactor too hard, especially if oversized compared to the systems demands, will see a depressed pH as the system volume tries to soak up the incoming low pH solution. Kalkwasser on the other hand raises pH as well as increasing both DkH and Calcium levels. In severe cases we can raise the pH locally in the vicinity of addition, so high that precipitation occurs, at which point both calcium alkalinity and magnesium may start to fall below natural seawater levels as they are bound into calcium carbonate. As soon as we stop dosing, the subsequently depressed DkH starts allowing the pH to drift again away from our target zone. It is commonly the case when combining both Calcium reactors and Kalkstirrer’s, to run the Kalkstirrer at night to offset natural biological pH suppression, and then switch to the Calcium reactor during the day, using the natural climb in pH to offset the addition of the low pH effluent. The main aim of this exorcise is to stabilise pH as much as possible, whilst boosting or maintaining Calcium and Alkalinity.

So how do we go about finding a solution to our suppressed pH?

First and foremost we have to be sure we actually ‘have’ a problem to start with, so chuck that 5yr old test kit in the bin, and go buy yourself a new one just to make sure before we go wasting hundreds of pounds trying to solve what may be a non-problem to start with. Secondly we have to be honest with ourselves and rule out those most common problems that stare us in the face. Look at your tank, and your last set of test results. Are your No3 and Po4 readings well above NSW levels regardless of that massive skimmer, Phosphate reactor and huge refugium? Are you blatantly over stocked for your given water volume or filtration capacity / skimmer rating etc, with greedy fish that require a lot of food for a relatively small volume of water? Whilst a heavy growth of corals wont place a massive demand on our o2 reserves, lots of fish, especially large greedy fish that expel a lot of waste like triggers etc, will place quite a high demand on the system, not only with their own o2 requirements, but also due to the amount of excessive bacterial action their waste generates. Ultimately in such situations, we have three courses of action we can choose from. Either a filtration upgrade to take care of the extra waste, in the form of a larger skimmer etc. A full change over to a larger system volume in an effort to reduce the overall Bioload to water volume ratio. Or a stock reduction, which lessens the load on the system at a base level. Whilst the filtration upgrade may at first seem the most financially appealing, we should remember that any such upgrades are only a temporary fix and have a finite capacity. Your fish on the other hand will keep growing, and keep demanding more food, so before we know it, we are back to square one again. So whether we like it or not, honesty with ourselves is always the first course of action. Are we simply expecting too much from our given volume of water or filtration system.

If we rule out overstocking and initial system instability, we are then left with a few more methods to get control of the situation.

1.The skimmer.

In many systems, the skimmer forms an integral link in the chain where the input of 02 and ridding of Co2 is concerned. Keeping the skimmer clean and working at peak efficiency will naturally help rid the system of pH suppression issues. Keeping venturi injectors open and free from calcium deposits will pay dividends as well. A final tweak that has seen great success in some instances is to extend the skimmer airline feeds to an external wall, and drill through allowing air to be drawn into the skimmer from outside. This pays particular dividends where o2 availability is concerned at night, as cooler night time air contains more o2 per meter/cu than warmer less dense air. The chart below shows a comparison on a 400 gallon, lightly stocked system, using external air to feed an AP702 skimmer on day one, compared to internal air on day two. The same test was conducted on alternate days to generate a trend.

............... 06.00........12.00........18.00........24.00........24 hr Drift

All measurements conducted using a freshly calibrated Deltec pH probe and Aquamedic pH monitor. DkH was monitored throughout the test and remained stable at 8.5 DkH. No changes were made to the system throughout the test period.

An average variance of 0.07 was encountered across the board, with occasional larger variances dependant on ambient external air temperature. The highest reading* was obtained on a cool day, overcast with a strong breeze. The lowest** was obtained with no external feed, and little to no ventilation in the room the tank was held. An interesting observation was that lower temperature night time air with its increased 02 concentration heralded a stabilising effect on the ambient 24 hr drift, minimising the effects of night time Co2 generation.

Posted Image

Feeding the skimmer external air can help resolve pH issues

2. Surface agitation.

As already discussed, surface agitation plays a key roll in gas exchange within any system. Pointing powerheads or other circulation devices at the surface is the most common way of creating this action as well as the less commonly used air stones. However surface area also plays a key roll in this as well. A tank that is wider than it is deep will naturally attain a more stable pH than a system that has a small surface area to volume ratio. Equally surface weirs will also play a roll in ridding the system of excess Co2 as water falls over the edge, mixing with air and travelling down to rush into a sump system.

Posted Image

Good surface movement encourages the transport of gases both to and from the aquarium

The table below shows the results of switching off all surface agitating pumps on the same 400 gallon system. The surprising factor here is how fast the change occurs. The tests were conducted over a 4 hour period using the same calibrated probe and monitor. No other changes were made throughout the test, and no food was added.


As can be seen, turning off the main surface agitation ‘regardless of the fact that the system was still flowing through the surface weir and sump system’ had quite a dramatic effect on pH, as gas exchange was limited to just the influence of the skimmer and weir. The differential after just 4 hrs* was a drop in overall system pH of 0.05 On the whole we wouldn’t see a perpetual drop in pH if we left the surface agitation switched off, as long as we had some degree of circulation present within the system. But what we would see is a marked difference in both our ambient average pH, and our day / night time drift.

Posted Image

Ph monitoring is made so much easier, and more accurate with a properly calibrated probe and monitor.

3. Room ventilation.

As with any animal, we breathe in air to extract o2 and expel Co2 as a by-product. In an enclosed space the relation of o2 to Co2 can shift quite dramatically. This can have an adverse effect on a tanks pH as it fights for the same volume of o2. Fitting a ventilation fan into the wall or ceiling of an enclosed fish room can see good results in the tanks ambient pH level, as well as a decrease in the amount of drift we encounter as cooler night time air is pulled through the system from outside, just as we did with the skimmer. Although the effect may not be as dramatic, every little bit helps. If the tank is in the same room as we live, then a window mounted vent, or open window will help minimise atmospheric Co2 build-up from having people in the same room.

4. Limiting internal Co2 generation.

Besides overall stocking ratios, we may also look at the amount of algal growth generated within the system. Whilst a reverse lit remote refugium does help minimise night time pH drop, we should still consider the effects of algal populations within the tank itself. Seeing as these algae are tied to the same day / night lighting regimes as the rest of our stock, they will have an aggravating effect on the overall drift encountered as they add o2 during the day, and take o2 at night. Having plenty of rudimentary grazers in the tank such as hermits, and snails to keep algal populations down will minimise the effect they have. Likewise efficient control of both No3, and Po4 are essential in this respect as they form the foundation of algae control at a free nutrient level.

5: In tank circulation.

As well as surface agitation, we should consider whether we have enough internal flow within the system itself. Good flow generates an effective mixing of the system water and balances out differences between o2 rich surface water, and water deprived of o2 that hangs around substrates. The knock on effect is that not only do we deliver this o2 rich water to the bacteria present, we also keep waste in suspension to make its way to the skimmer or other filtration devices for removal before it gets a chance to break down. This has a Knock on effect throughout the whole system, both in terms of free nutrient levels, in tank algal populations, and bacterial populations in relative proportions to the amount of stock we have and the food demands of the system. All of which take a toll on our pH reserves.

6: chemistry.

Last and by no means least we have that inescapable quandary for many reef keepers, i.e. how to get to grips with the water chemistry. By and large you don’t need a science degree nor any great level of understanding to get to grips with reef tank chemistry, as long as you follow a few simple rules. Always buy good quality test kits that are ‘in-date’. Always follow test procedures to the letter and conduct twice if you’re not sure of the reading. And never act rashly to an erroneous reading no matter how serious it may seem at the time. In relation to pH, a properly calibrated probe is by far the best way of accurately measuring. Most problems with pH are commonly attributable to either, test kit inaccuracy / poor quality or an incorrectly calibrated / neglected probe. Keep your testing equipment organised and in good condition, and you’ll rarely have any problems where you need to double check with an alternate source such as a shop or fellow reef keepers equipment. But even still, its worth having a backup on hand should you encounter something your not sure about and need to double check before taking action.

As already covered, there are several key components to sea water that have a direct influence on how your system maintains a stable pH or ambient pH level. By getting familiar with the three main contributors, namely Alkalinity, Calcium and Magnesium, and logging your test results, you can determine the systems demands to ascertain which of the various dosing regimes are most suitable for you, be it from simple water changes in low demand systems, to full blown Calcium reactor and Kalkstirrer set-ups for high demand systems. A few simple rules will ensure long term success. Never change parameters too quickly, as the knock on effects will usually happen faster than you or the rest of your stock can keep up. And always read the instructions on any additives / supplements you use to effect a change in chemistry. Multi part additives are no use for boosting a ‘single parameter’ as they will affect other readings as well. If you keep your chemistry balanced in accordance with natural sea water levels, then by and large the system will reward you with expected results.

So hopefully, this article has given you some areas to focus on with regard to pH issues within the reef tank. Above all though, it is strongly advised that any changes are made in a logical fashion and very gradually when it comes to pH or other chemistry issues. But be honest with yourself first and foremost. Over stocking is the number one cause of pH suppression in most instances. You can only get so much out of a given system, and you can only place so much Bioload on it before it starts struggling, so maybe it ‘is’ time for that bigger tank you’ve been promising yourself after all.

Simon Garratt.

( All images and text copyright Simon garratt 2008)

Simon Garratt O.C.R.D

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users