pH difference between tank and tap

[the_deeb]

My aquarium has gone completely out of wack since changing my filters and I've been doing lots of water testing. I just found that the pH of my aquarium water looks like it is at least 6.0 (the limit of the test kit) whereas the water from the tap is close to 7.2.

I know this is often a sign of old tank syndrome but I'm pretty good about WC and recently the tank has been getting 25% changes twice a day for the past week since I've been trying to combat an ammonia spike, so I don't think it can be blamed on detritus breakdown.

Any idea what's going on?

 

[Pufferpunk]

Ammonia--keep up with the WC & it will equal the tap water eventually. You may need to do more than 25%. Are there fish in there?

 

[ar0wan]

What are your kH readings? You're ammonia is certainly contributing to the pH drop, sounds like you destroyed your bio filtration completely. The tank will cycle out and return to normal soon.

 

[the_deeb]

I thought that might ammonia might be the problem, but my ammonia readings have been at 0ppm for the past few days.

It just occurred to me though, doesn't amquel interfere with the ability of some test kits to detect ammonia? I'm using the Aquarium Pharmaceuticals test kit. I've been treating the aquarium pretty heavily with amquel given all the water changes. 25% was probably being conservative - probably more like 40%.

There are fish in there, but they're not doing well. I skipped an evening water change two days ago when it looked like the ammonia reading had stabilized and ended up losing the last of clown loaches this morning There are currently 4 young geophagus in the aquarium that have pretty bad ammonia burn on their eyes.

 

[brianp]

Within a healthy, active aquarium, there are several natural phenomena which can cause the pH to drop over time. For example, when the fish discharge CO2, this reacts with water to form carbonic acid. Of these phenomena, I think ammonium being reduced to form ammonia is minor in effect. Water changes can be somewhat effective in restoring the pH, but then you have a roller coaster effect and are subjecting your fish to ups and downs in pH. If you simply add a little bit of baking soda (sodium bicarbonate) between water changes, this will help to stabilize the pH until the next wc. It doesn't take much. Also, if your fish are estuarine or brackish or like salt (for whatver reason) you can add something like Instant Ocean to your change water. Synthetic sea salts contain buffering agents which will allow your aquarium water to resist a decrease in pH. Others have advocated adding crushed coral (calcium carbonate) to the filter to act as a buffer. A gradual pH decrease over time is NOT indicative of a problem with your tank....it is natural and anticipated.

 

[the_deeb]

Unfortunately there clearly is a problem with my tank (based on all the dying fish). Whether or not the pH difference is contributing to it is not clear.

Also, after thinking about it a little, why would ammonia lower the pH of the water? It seems to me that NH3 should buffer an H+ and become NH4+, thereby raising the pH. Am I missing something?