© Albert J. Thiel - September 1997
Not so infrequently, hobbyists struggle with a pH falling syndrome over a period of time that can occur at any period in the lifecycle of the aquarium. Their pH may be too low to begin with when they just start their aquarium, and/or if may become too low even after the cycle is just completed. As the tank ages, the pH may suddenly start to take a drop and often the hobbyists is at a loss to understand why.
The falling pH syndrome can "really" occur at any time in the life cycle of the aquarium. The fact is that it does happen and that many hobbyists are at a loss understanding how to counteract this chemical tendency. There is nothing unusual and nothing dangerous about this as long as you catch it soon enough and take measures to bring the pH back up. This document and others in the NetClub Library explain how to do so.
We all know that water quality varies. It varies a great deal in fact. Even water quality readings taken in the morning will not match up with readings on the water chemistry taken at night on that same tank. This is a normal occurance and results from all the chemical and biochemical processes going on in the aquarium. Note also that we do not have any control over most of these reactions.
This can be attributed to various causes, many of which are not always that obvious to the hobbyist:
The pH of an aquarium is an expression of the relative presence of acids and bases in ionic form. What happens is that when the amount of acidic ions (to phrase it simply) outnumbers the caustic ones, the pH of the water will be low.
The opposite is, of course also true: when their are more alkaline ions in the water than acidic ones the pH will, naturally, be higher.
Depending on which ions are more prevalent, your pH will tend to be either lower or higher.
Since it is known what affects the pH, it is possible for you to intervene and add certain compounds to the water to make the pH rise. These compounds are those portions of the buffer that have a tendency to push the pH upwards.
Carbonates and Borates will make the pH rise. Bicarbonates have a tendency to make the pH fall.
The mixture or the proportion of these compounds in relationship to the total buffering compounds (the % of each) tends to influence where the pH will stabilize itself at.
If your aquarium has lots of bicarbonates in the buffer, yet few carbonates and borates, the pH will be more influenced by the bicarbonates. As we have seen this will lead to a low pH level.
It should be obvious by now that having the correct proportions of these buffering compounds in dissolved in your water is important and is what ultimately ensures that your pH will not demonstrate a falling tendency.
Our task, therefore, as hobbyists is to adjust the buffer in such a manner that the buffer contains all necessary compounds and that these compounds are, and remain, present in such quantities that the pH does not drop to levels lower than we wish it to be.
As the explanations above made rather clear in my opinion, a distortion in the make-up of the buffer can, and will more than likely, result in a drop of the pH level. When this is just a simple distortion, rebuffering the water with a complete buffer (one that contains all 3 compounds mentioned earlier) will re-establish your pH. Your "only" task is to add enough buffer, slowly, until the desired pH is reached again.
You then observe the pH for a few days by testing it, and add more buffer, if necessary, until you are satisfied that the pH has stabilized itself and no longer fluctuates downwards. Theoritically the pH should be at its lowest in the morning and should slowly rise as the day goes by and photosynthesis takes place. Since this removes carbon dioxide from the water, the pH will have a natural tendency to rise. Towards the end of the day the pH should be higher than it was in the morning.
What was just described is the simplest of all the possible scenarios. Unfortunately, it is the one least likely to occur. More often than not, the problem is deeper rooted and a far greater intervention on the hobbyist's part is necessary. The low pH problem and the process associated with resolving it, is more complicated and will certainly take a longer time to solve than the one just described where only buffers are added to solve the problem. When the pH is out of balance for several reasons, the solution is obviously much more complicated, as we shall see later in this article.
When the pH is low, and is low on a continuous basis, your problem is of a totally different nature. In fact it is, more than likely, due to a combination of circumstances, each of which may require a totally different approach, or it may take a combination of methods to really solve your problem.
Sure, adding more Limewater (Kalkwasser) to the aquarium is going to raise the pH (see document on Kalkwasser), but this is only a temporary patch. Often, however, even the addition of KW (Kalkwasser) will not solve your problem. We shall later in this document that the only way to truly stabilize the pH and have it maintain a healthy level is to deal with the root cause of the problem and solve it once and for all. You need to solve your buffering problem and then go from there onwards.
Kalkwasser raises the pH. There is no doubt about that but it does so in what I would call an artificial way by adding a lot of hydroxyl ions (OH) to your water.
As long as you keep adding KW (limewater) your pH will remain at a high level, even if your dKH is low. There is a caveat though, if your dKH is really low you may have to add so much Kalkwasser that it is not really possible to do so because your evaporation rate is not high enough.
This would mean that you would have to remove additional amounts of water from your tank to be able to add more Kalkwasser. This is, obviously, not a viable solution. It does not make sense to have to take out water from the aquarium to be able to raise the pH but only do so artificially There has to be a better way.
Because the whole buffer is out of balance the first thing we need to do, if we are to hope to achieve pH stability, is to deal with this in a radical manner by undertaking a few important steps
Changing water in the tank is going to gradually bring about the alteration of the water chemistry we are looking for to bring your buffer and your alkalinity (dKH) back in line. I have described below how to proceed to obtain success.
All the water changes your are performing, or have by now performed, will have affected the water chemistry in many ways.
Most importantly they will have re-established a proper balance of the buffering compounds within your tank. The proportion of bicarbonates, carbonates and borates should now be back to normal and the pH of your tank should have increased.
If you now start adding (dripping) Kalkwasser to your tank, you will find that the pH will rise even further. This is because calcium hydroxide, mixed with water, makes the pH go up. It is important to realize though, that KW needs to be dripped continuously and not added all at once (or certainly not as powder to the sump). You can however drip the milky KW solution into your sump or tank rather than a clear solution
How much KW needs to be added depends on the evaporation rate of your tank. If this evaporation is low, the amount of KW you are adding may not suffice and you may need to add additional calcium in some other chemical form. There are several such products available commercially.
There is the possibility that after all the water changes and even though you add KW and maybe another calcium compound, the pH still shows a slow drift and tends to go down.
This is easy to remedy. It is discussed in the next section. In most cases you will not need to resort to this, but the possibility does exist.
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© September 1997