ph drop! help!

Question
I have a 20 gallon tank that I just set up a little over a week ago, with just one electric yellow lab. I used the old filter, gravel and decorations from the original 10 gallon so I wouldn't have to go through a whole cycle again. Because I upgraded tanks I've been checking the water every couple of days, origionally my pH was at 7.5 (not ideal for yellows, but I know it's better to leave the pH alone than to shock the fish) but after getting my water tested again today the ammonia was fine but the pH had dropped to 6.4! I haven't done any water changes yet...what could have caused this and what can I do to fix it? Please help! I don't want my fish to get stressed or die.

Answer
Hi Katie,

I had my response all typed out, but then my computer crashed! Grr! Ok, let's try this again.

First off, it's going to help you out a lot in the long run if you write down the water chemistry of your tap water. Take note of what the alkalinity, hardness, pH is and if there are any nitrates. If your tap water is usually 7.5, then something happened to make it quickly drop down to 6.4 - the solution is to do a big water change, about 50% or so. This will replace whatever minerals were expended that caused the buffering capacity of the water to fail.

If you are using municipal tap water, it is not unusual for it to be low in alkalinity. The best thing I ever did for my African cichlids was move to a house with well water. Now my water out of the tap has no chlorine, a pH of 7.8 or so, and very high in alkalinity and of a moderate hardness. The alkalinity is key, because it is alkalinity that buffers pH.

Fortunately, there are ways to artificially add buffering capacity to your aquarium. The easiest is to use crushed coral. I use crushed coral and aquarium gravel 50/50 on my cichlid tank and it works well. The cichlids also like to sift through the sand if they can reach it! Oyster shells work too, but are harder to find nowadays. Personally, I recommend you use crushed coral. Blend it into your substrate. You can also add about 1/4 teaspoon of baking soda to each gallon of aquarium water you use for water changes. This will work for a while, not as long or lasting an effect as the crushed coral. You can read more here:
http://www.aquahobby.com/articles/e_adjusting_pH.php

I hope that helps, take care!
Nicole

P.S. One site I recommend for cichlid information is:
http://www.cichlid-forum.com

It's comprehensive and searchable! Be careful what you mix with cichlids, since I assume you will add more fish eventually. Electric yellow labs are some of the mildest of the mbuna, but an African cichlid is an African cichlid after all...no bettas or guppies in that cichlid tank!