1) 55 gallon

2) Two indwelling hanging filters

3) About 20 fish (platies actually) plus 3 cory

4) Ammonia 0

5) Change 20-25% water every 2 weeks (water bill too high at weekly, though I prefer it).

6) pH in tank water..6.6

7) pH from tap water 7.0-7.1

8) Decorations: Gravel, synthetic fish decorations and plastic plants (ie: no real rocks)

What in the world is causing my pH to drop so low? I've been adding pH up like crazy and it's not helping (almost 1/4 bottle in a few days) very much. I don't want to rush it because I know it's not good to raise too fast, but the poor fish are seen sometimes gasping at top for air. I have tried buffers in past but not much luck with them, so not much faith in them (though may try again here soon). I do have a TON of algea in the tank...is that causing the pH to drop or is it blooming because of low pH? (I clean it all off 3 sides and leave it alone on the back wall). I would LOVE ideas. I can't find any in IH.

Could this also be why not many of my babies live, despite a TON of plants?