Originally Posted by Xhilr8
Can somebody help me out here... I have a problem with my tank where I cannot seem to raise the pH above 7.8 no matter how much buffer I put in or how many water changes I do.. The lady at the LFS
did a test on my water and said the water was too hard (I assume she was referring to the KH
or carbonate hardness). Correct me if I'm wrong, but does kH
and alkalinity refer to the same thing (generally speaking)?
Water hardness (often expressed in GH
) basically means it has more minerals in it. Primarily Magnesium and Calcium. In a SW
environment, the GH
is not relavent and the two must be measured seperately to guage the balance against the KH
or cardonate hardness often expressed in terms of DKH
(Degrees of Karbonate Hardness) or mEq/l of alkalinity.
And if alkalinity or kH is high, does it mean that it will be difficult for the pH to FALL as well as INCREASE? I thought that if kH/alkalinity is high, it means that pH just wont fall but you can increase it if desired by using buffers.... although buffers do not seem to work for me.
Alkalinity is a measure of the waters ability to resist changes in pH but does not necessarily mean it can control the pH just help maintain it. The use of buffers will often raise both and a proper alkalinity (1.5-3 mEq/l NSW
) will help keep pH stable.
If using a buffer to raise/maintain pH you are also greatly increasing the alkalinity at the same time depending on amounts. If alkalinity becomes too high, you will run the risk of damaging the organisms within your ecosystem as well as bottoming out the Ca
due to Magnesium precipitation.
Often, the solution in these cases is environmental and not chemical. Having your LFS
test your waters pH is actually futile. Once removed from the tank for any length of time, CO2
affect the levels and skew the results. In cases of low pH and avg-high alk
, the problem is most often poor gas exchange. Usually from a covered (sealed) tank, insufficient water flow, overstocking, overfeeding or some part of all. If this is a cycling tank, there will be constant shifts in the pH to the lower range due to the higher acid production from the higher ammonia source which utilizes much of the available O2
pH is also effected by the time of day tested. In the earlier parts of the day
especially before lights on, the pH will tend to be naturally lower to to the algaes producing CO2
at night. Throughout the day once the lights are on, the same algaes begin to produce O2
allowing the pH to naturally rise up. The best time to test the pH is tyically middway through the photoperiod. You can test in the morning and later at night to determine this yourself. Whenever you do test the pH, always try to do it at the same time of day. That will help determine the stability
of the pH.
I would suggest a small test. Remove a small cup of water from the tank and let it sit uncovered for about an hour. Test the water from the cup and then test the water from the tank and compare. If the hour old smple is much better, it is most likely something amiss with the set up.
I would also suggest posting some more detailed info about your set up. Have you purchased an alternate pH kit to see if the one you have now is faulty?
The Relationship Between Alkalinity and pH
.... by Randy Holmes-Farley