pH

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jhnrb

Reef enthusiast
Sodium Carbonate

At times the pH in your tank will have a tendency to drop and slowly lower itself for no reason that is apparant to you. All water quality parameters seem to check out correctly, even the dKH, yet the pH just does not want to stay at recommended levels, in fact, in most cases the pH has a tendency to fall to around 7.8 or 7.9 and regardless of what you do.

It does not rise even though you may be adding lots of Kalkwasser. In some instances you try to compensate for this by adding milky KW but all you obtain is a temporary rise in the pH and then it starts to fall again.

This happens over and over again.

The main reason for this unexplained drop in pH is the presence in your aquarium water in dissolved form of a variety of acids which lower the buffering capacity and skew it. What I mean by this is that the bicarbonate portion of the buffer may still be high (hence your normal dKH reading) but the carbonate portion is low (hence the low pH as carbonates affect the pH much more than bicarbonates).

The solution to this problem is to neutralize the acids and then build up the carbonate portion of the buffer again. This is done by slowly adding sodium carbonate.

At first when you add this compound the pH will go up. As it reacts with acids of various kind it becomes neutralized and so do the acids and the pH drops again. As long as this rise and fall continues, you have not neutralized all the acids yet and you need to continue to add sodium carbonate until the rise continues but the drop starts to become smaller or dissappears (at which time you know you have neutralized the acids).

This "can" be a frustrating experience as you may need to dose with sodium carbonate for quite a few days before you actually see a change occur and before you start to see the pH rise and stay in the higher ranges.

All you need to do is persevere and you will eventually get there. The pH will rise and stay at the higher levels and the acids will be neutralized.

You are probably wondering what kind of acids make this happen. Mostly they are of organic nature and include all the amino acids which result from the breakdown of protein (another reason not to overfeed and to have a real good skimmer), but there are also other acids present: carbon dioxide, boric acid and phosphoric acid amongst others.

Before all of these are neutralized some time may go by. Do not get discouraged. Continue to add the sodium carbonate and you will eventually get the pH and the buffer under control.
 
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