Good shout
@Wile e Peyote dude there is something in liquid silica that helps stabilise ph.
Dont just get it and throw it in the res now though... if you do it will put ph up through the roof.
I use it as ph up when i accidently put too much ph down in!
Also depending on what nutrient brand you use the order you add nutes to the res can have an effect...
I use ghe flora trio and i have to start with micro give a good stir then add grow and give a good stir then bloom last.
If i just threw them all in together at once certain chemicals from each bottle bind together and form something new that the plant cant use and that can mess with ph too. I always used to wonder why we needed so many bottles!
Thats what the nute companys say anyway.
So i go base nutes-calmag-silica-hydroguard-bloombooster(in flower)
Give a good mix between every bottle then use ph down and check.
Sorry to rant on if your already doing all this mate.
I like to keep an airstone in my res too just to keep the solution moving around a bit but a lot of growers say that csuses their res ph to climb as well