I have a problem with my 37 Gallon tank. It seems I keep losing guppies every other 2-3 weeks. My water parameters are good PH 7.2 or usually kept over 7.0 Ammonia 0ppm Nitrite 0ppm Nitrate 0ppm I've had nitrate go up to 0.5ppm, fixed it, and PH drop occasionally. I've come to a conclusion that it has to do with my PH, blaming driftwood for that. Or maybe I'm not doing my water changes correctly. For water changes I mixed faucet water with my drinking water and add seachem prime and some stress coat. The guppies would act "lethargic", and hanging out by corners then eventually die. Any input or suggestions to this would be highly appreciated!