Stabilizing PH - How often?

Hello, I am a long time soil/soil-less grower, looking to try DWC for the first time - here is my question -
Is it normal to have to adjust the PH as often as every 12 hours? I ask this because I adjusted ph to 5.7 last night at lets say midnight it was high around 6.5. I just checked it and its back at 6.5. What is this? the water level has not changed. this is straight PH'd water.. is this normal?

I should clarify, there is no plant yet. this is just the bucket with the hydroton, a rockwool cube, and a seed in the cube.

I think I may have just found the answer in a similar thread - http://rollitup.org/t/ph-dropping-in-dwc.955356/ - Looks like I have most of the answers I need here too.

THT said:

Hello, I am a long time soil/soil-less grower, looking to try DWC for the first time - here is my question -
Is it normal to have to adjust the PH as often as every 12 hours? I ask this because I adjusted ph to 5.7 last night at lets say midnight it was high around 6.5. I just checked it and its back at 6.5. What is this? the water level has not changed. this is straight PH'd water.. is this normal?

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I set my ph and it will hold for three weeks dropping or raising by no more than .1 ph. I set mine to 6.5 and after a few weeks it’s dropped to 6.3. I simply use my well water ph it let it warm up to 68 degrees and recheck it after a day then add my nutrients check then add it to my 55 gal Rez. Being a rdwc the flux of the water is minimal however I’ve done the same. Running 5 and 13 gal dwc set ups

Once a week done with rez change

Thanks all, I have found that it is easier to control when the EC is a bit higher i was running at about 90ppm, ive upped it and it has been much more stable. also I am only using a 3 gallon bucket!

THT said:

Thanks all, I have found that it is easier to control when the EC is a bit higher i was running at about 90ppm, ive upped it and it has been much more stable. also I am only using a 3 gallon bucket!

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ya, with just the water and no nutes/buffers...its gonna swing hard.

I use pH Perfect nutes and never think about pH or check it at all.

Before they came along I'd pH down with conc. sulfuric acid to around 5.5 and 3 days later after topping up with RO water it would be around 6.3 so would add 4 or 5 drops of acid to make it 5.5 or so again. After a while I just added the acid at every top up and checked the ppm and adjusted that. A pH swing is good for nute absorption or so it's said.

Start at 5.5 then adjust at 6.3. If ur doing this more than once a week u should think about getting a bigger res