well for the past week and a half i have lost 3 fish, been testing water always same results its a FOWLR tank. ph 7.9 nitrates 20-40ppm nitrite 0 ammonia 0 my fish never seemed stressed out, ate good, ik no chemicals got into it cause im the only one that messes with the tank and does the pest control in the house and i dont spray the chems in the room its in. the fish dont seem to have been beaten up. i use instant ocean salt. my ph always sat around 8 but would a .1 deff hurt them. idk what is causing it to drop ik i have good o2, co2 exchange on the water have an air stone in sump for that and the skimmer running always seems to be pulling good amount of skim off. this all started after i did a water change with my ro/di system (first time using it) yes i followed the instruction to let it run 30 mins before using it for anything. now this is just discouraging me from doing any other projects. i never had a problem till i did the water change with the RO/DI system.