hello everyone i just got a new 300liter res and im having some problems. I adjust my ph to 5.8 and when i come back the next day it jumps to 7.5 sometimes a bit higher. Now i have used almost half my ph solution bottle in the past 3 days keeping my ph right. Anyone have any ideas?

i have a 300l airstone in there and nutes are advance nutriets and i also put hydrgen peroxide in.

I turned the airstone off today just to see if thats what is making the ph fluctuate.

If you are using tap water try testing the ec of the plain tap water. If it's high you have hard water and the calcium carbonate neutralizes the acid. Are you also getting a white powder?

I am on RO water. dont think so on the white powder. dont exactly know what u mean but the answer is no white powder

RO water should have a PH of 7 to begin with. I don't know if the acid you are using could somehow be reacting with the peroxide. Another possibility is that you are not adequatly mixing the acid and allowing it to stand for a while before testing and getting a false reading. Then again if you have certain microbials in your root zone they could be causing that problem. Are your roots white or brownish?

What is the EC/ppm of your nutes, and when you say pH solution do you mean a phosphoric acid based product??
RO water is actually tougher to stabilize than harder water because of the lack of buffering compounds.. Phosphoric acid reacts with alot of stuff to form some excellent buffering agents in the 6-7 range..
Its not the H2O2.. Any pH shifts caused by that are going to be short lived.. My guess is your nutes aren't providing adequate carbonates etc for the pH down to do its job, and they aren't in the water..
One thing that increases buffering capacity nicely is peat.. Soak some peat in your res, and the pH will fall, and tend to be more stable in that range..

Do you think i should just pump out the water clean the tank and start over?

No, it can only get better..

You are over simplifying it a bit. First, H2O2 can give of a highly reactive singe O atom and it's hard to predict what kid of issues that can cause.

Secondly, buffering prevents shifts in PH in both directions, not just upward. And you don't want to create a heavy calcium phosphate salt issue in the name of buffering. Those heavy salts can also push the nutrients out of solution causing toxic conditions.

Pure water should change PH quickly with the addition of acid. What may be happening is that he has some microbial conditions that are causing a rise in PH.

I'm guessing its not buffering it high, that it shifts at a fairly steady rate across the swing.. I guess its not a bad idea to ask how many drops of pH down it takes to drop from 7.5 to 7.0, compared to 7.0-6.5, compared to 6.5-6.0 and so on..
Microbial action tends to drop pH, and he's tossing H2O2 in there so I doubt that.. And furthermore, H2O2 effects would be short lived, especially in high pH solution..
As for buffering, it depends on the compounds doing the buffering, and the current pH as far as buffering directional capacity goes..
Hydroponic fertilizers usually contain alot of nitrate N.. Uptake of this lowers the [H+].. Hydrogen/dihydrogen phosphates are supposed to combat that..
And wtf are you talking about pH down byproducts pushing nutrients out of solution?? Study up on your solubility charts..

the ph is at 7.1 now and 50 ml of ph down in the 300 l tank barely makes it move down.