So I have a 20 gallon long tank my reading are good for except my Ph. It is extremely acidic. I bought a ph drop test kit and I test my water source and my water source has a 7.4 ph but my aquarium water is like 6.0 or worse. My fish are fine and keep swimming and active but my ph worries me any reason as to why it is low? It has a aqua filter 10-20, 5-15 , top fin 10. And fish are 2 dwarf gouramis and 4 zebra danios and 4 rasboras