I have a ten gallon that is recycling after a bad experience with some algae destroyer.Wiped out the bacteria,then most of the fish died of ammonia poisoning.
Only fish in the tank are 1 female betta,1 zebra danio,1 mystery snail.
the cycle has reached the point of producing nitrogen so I added some low light plants.That was last week.Yesterday i did my water change,(20%)and ph was a perfect 7.0.Today it has dropped to below 6.0 . Ph up by API does'nt seem to be effecting it at all.



Here is the plant.Can't remember the name.

You may find the answer to your problem in "Aquarium Chemistry 101" which is a pinned topic in this forum.

I personally do not use any of the ph rising or lowering drops, I learned a long time ago that they are a waste of time and money, and they didn't work for me. None of the fish I keep are that fragile and they are happy as long as the ph doesn't fluxuate wildly.

your better off fixing the source of the problem with algea then using chemicals on it and letting the tank adjust itself slowly. when you introduce drastic changes like that you find yourself fighting to keep up with the reprocutions...as you've discovered.

My theory os the ph drop is most likly in the water change, if you use tap water without letting it sit it can do that, they add chemicals it exits the pipe at a certain ph, but that is almost always unstable. I do water changes half RO water half tap thats sat in a bucket. but my tap water quality is very good here.

unless of course you added substrate like peat for the plant, that will lower ph too

No peat.Water quality is horrible.Ph out of the tap is off the scale.i.e. it takes 2 drops of ph down per gallon to drop ph balance from,say,6.8 to6.6.I have to to use 10 drops per gallon just to get it down far enough to register on the scale.I will not discuss water hardness except to say it almost qualifies as a blunt instrument.

I'll see what I can tell you. I have an extensive back ground in water quality and I do not know your own knowledge level so if you need any clarification just ask. Needless to say sometimes I am able to say things in English and other times not.

Reasons for pH drop:
The nitrogen cycle - acidic bi-products at all stages.
CO₂ - plants need it, however it can crash pH
Low KH or carbonate hardness which when combined with this other stuff will easily drop the rest of the way.

Try this experiment, measure your pH KH and GH right before lights out, then measure again when the lights first come on and one last time when they shut off again.
Label the first one as lights out and the second as lights on.

I would expect that the pH and KH should experience the greatest change with the lights off when the plants go from producing oxygen to carbon dioxide.

Additional thoughts would be along the lines of how well trimmed the plants are, the nitrogen cycle is affected by more than fish poop, anything breaking down will contribute.

When you get back we will probably be able to come up with a true solution.

Thoughts:
If the pH is crashing at night then you may need to add an air stone on a timer set to kick on shortly after the lights kick off and kick off a little after they come back on. This will help reduce excess CO₂.

Add 1/4 teaspoon of crushed coral to a filter in a nylon or media bag. Let this run a day and see if it makes a difference, if not increase another 1/4 teaspoon until it brings the pH up slightly above neutral. Watch this one carefully if you try it, you don't want your pH above 7.6 I was thinking 7.0-7.2 with a little KH to buffer would be nice.

I found the problem.although I had remove the little plastic basket from the plant ,I left it in the gowth medium.It was peat.Idid'nt recognize it because it was so bloody pale.

Thanx for help guys.

Glaive,you have given me some interesting experiments to try anyway.