Low PH

This is my first post here. I'll try to be brief!

I have two 10 gallon tanks at the moment. One has cherry shrimp and snails; the other has 3 black neon tetras, 2 african dwarf frogs, and 2 cory catfish. Both tanks have been running for about 6 months and have lots of nice healthy plants and moderate lighting.

The pH is 7.2-7.4 in the shrimp tank (ammonia= 0, nitrite= 0, nitrate ranges from 0-5). There are loads of bad snails, and my apple snail is not doing well. Shrimp are thriving.

But the fish/frog tank is more unstable. Ammonia and nitrite are consistently 0, but nitrates go up and down from 10 to 40.
And the pH has been at 6.2 for months. (It used to be over 7, but after 1+ month over the summer without water changes, it plummeted and has stayed down). I do weekly 15-20% water changes, using prime and replenish. And I fertilize the plants with liquid fertilizer every week or two (which seems to help when nitrates spike).

Everything seems healthy in this tank (including a mystery snail), so I am reluctant to make major changes if I don't have to... but I need to transfer its contents to a new 20 gallon long tank soon (just bought and still need to set up) so I want to make sure all my parameters in the new tank are right, and not shock the fish/frogs in the transfer.

Can anyone please advise?? TIA

tanker said:

Over crowded??, depending on how big the corys and frogs are. Over feeding??

Click to expand...

Perhaps. Definitely possible for the over-feeding. The fish are fed 2x/day just a few flakes.
But the frogs are fed bloodworms in a bowl 3x/week, and there is a lot of mess because the corys stir it all up and it gets into the gravel.

If part of the issue is overcrowding, moving them all into a 20 gallon should help. I will start setting it up and cycling it this week. The new gravel is actually plant substrate, so it should be smaller and have less gaps for worms to fall into.
I'll move some plants, water, and filter media from the old one to the new. I won't move the fish/frogs for a few weeks. How should I acclimate them from the low pH to the new tank, which presumably will have a more neutral pH?