I am new to this board and I am having a hard time trying to control my PH Level. No matter what i do it always reads 6.0 or lower. First I am using a PH test kit from API, But I have also brought a water sample to the pet store where I get my fish. I have a 40 gallon freshwater community tank. I have less than 40" of fish that I am allowedfor the size of my tank. I have used Nuetral Regulator made by Seachem and PH Increase from TopFin ans I have started to use it in moderation as to not shock the fish and the first dose turned the water pink. the second dose made the water turn orange.The most it goes up is 6.4 and returns to 6.0 by the next day. I am loosing fish every once in a while. I am not over feeding them. My ex is getting ready to tare down her tank and give me othe fish, but I dont want to put them in a tank that is like that. I bought the tank used with all of the gravel and Fluval filter.I`did cleaned it out thoroughly but with no cleaner. I do a 40% water change and clean with a Python so the gravel is clean. I have used the water conditioner and without it and there is no difference. The water from my tap is 7.4 and I test it 2 hours after I change the water and it reads 6.0 I also check it the next day and its the same. The guy at the petstore has been in business for 20 years and he is stumped. He thinks that its either the tank was cleaned with something or its the gravel that is causing this problem.