PH

Running an ebb & flow with a 40 gallon res. My tap water is coming out of the tap at 8.3, but after 24 hours aging tests 7.8. I am using general hydroponics PH down to lower ph. My res ph after adding nutes (actually mixed 5 gallons at a time) was 7.3. I used 1/3 of an 8 oz bottle to to get it to 5.8 last night. Then when checked today back up to 7.1, there had been 2 15 min cycles between checks, and I had to add another 1/4 bottle to get back to 5.8. I understand my ph can go up after feedings because I am using rockwool, and they have actually only been "fed" 3 times now, at 33% strength. But, my concern is.....it seems like it is taking alot of ph down to get my water where I want it. I add it 10ml at a time.....so believe me it is a slow process. Any suggestions?? I have RO filter in at local store, but cash tight right now. Will buy soon...but until then...should I just keep doing what I am doing or is there an easier, softer way to get my ph down??
I sure hope someone answers me.......seldom get much response. Oh well.

I never liked GH's pH Down, but it is better now than it used to be. My water is similar to yours, and for 4 gallons it takes about 10ml of Down plus nutes and additives to make it 5.8, and then 2ml of Down the next day and it's set.

So for 40 gallons, that would be 100ml, or 3.6 ounces, about the same that you are using.

I use a pH Down that is 30% phosphoric acid.

What nutes are you adding, that can make a difference in the rebound.

HTH

hell i went to walmart and grabbed the big buckets of ph up and down granules... those are working awesome and i am able to get it to the 5.2 every time... i practiced with a 1/2 teaspoon measuring spoon ... it only take a very little bit... but i do notice that i have to adjust daily..... good luck

also.. i cannot explain what a big difference buying RO water makes... when i first bring it home the waters ph out of the machine is in the 5.2-5.8 range... after a day or so of sitting in the 5 gallon jug it creeps up to the 6's... mid 6's... dude 35 cents a gallon cant hurt you that much...