So my ph in all my 4 tanks is 7.5ish well I checked all my tanks with a test strip just for the heck of it (even tho I have api master test kit) and all of them said 7.5 besides one... my 20 gallon. It read 6.2!!!!?? I have to admit I fall behind on water changes but I have plants in there so nitrates don’t really rise too high. What could be the cause?? All my fish are acting fine that I’ve had for months and I’m scared if I do a water change the ph from the new water will shock all my fish i need help!!