I dont mean to be rude here - but i dont know what your water is like there - what qualities it has, but i use PH up and PH down, and my PH does not YO YO as you put it.
I move the PH as i require it, and it stays fairly close to that reading.
Our tap water comes out at around 8.2 PH - (much too high for freshwater fish), I add ph down in small amounts and keep testing until it is close to where i want it to be - around 7.0. The tank water stays pretty close to this until i do a water change (allowing for small natural shifts from natural biological processess within the tank).
I move the PH as i require it, and it stays fairly close to that reading.
Our tap water comes out at around 8.2 PH - (much too high for freshwater fish), I add ph down in small amounts and keep testing until it is close to where i want it to be - around 7.0. The tank water stays pretty close to this until i do a water change (allowing for small natural shifts from natural biological processess within the tank).