Sudden PH level drops.

Question
Hello, thanks for your time.  I've had the same fish for about 4 years now.  I had originally had a very old long narrow 60 gallon tank.  One year ago I upgraded to a newer 55 gallon tank with a curved front.  The fish that are currently in my tank are a Texas Cichlid, a Brown Knife and 2 large Pleco's.  About 1 month ago I started experiencing some pretty drastic ph drops. The tank normally sits around 7.0-7.2.  It is now around 6.0.  I havn't changed the way I care for the tank in the many years that I've had it.  To try and fix the problem, I've been changing approx. 20% of the water every 2-3 days, however, the ph is not changing at all.

I have rock gravel as the base and various plastic plants and decorations as well as a couple decorative pet store bought aquarium rocks and some limestone rock.

The fish have become very sluggish, they will no longer eat their normal food (flake food), the only thing they will eat  currently are frozen blood worms.  (These were in the past given every now and then to the fish, not on a regular basis.)  Both fish will approach the flakes, ingest them then spit it out.

Any help you could give me would be wonderful.

Thanks again.
Derek

Answer
HiYa!

Ok changing your water will not raise your PH in fact it may do the opposite and drop it futher.

Having limestone in your tank is a good start as it acts as a buffer but I'm presuming if your PH has dropped then your KH would have dropped too which is why your fish are sluggish and off their food.

Add 1 teaspoon of KH powder to your tank over the course of 3 days and then test your PH again to see if it has raised. During this time DO NOT DO any water changes. If your PH has not raised to what it was sitting on before, add another teaspoon of KH powder and test the day after. (When adding the KH powder, mix it with some water from the tank in a cup and then pour it in, it saves it landing in clumps on the gravel on the bottom of the tank and some fish eating it...which they do!)

Hope this helps!

Cheers! Rach