I just ran out of ph down, and I went and bought some battery acid for $12.99 for 6 quarts. It’s all they had lol, and one gallon of distilled water. Followed your directions, take out 2 cups of water from the gallon, added 1 cup of acid. I’m letting it settle and mix on its own. Then I will test it out.
According to my math it should give me 24 gallons of ph down for $40. A gallon of distilled water is about $1.
Concentrated sulfuric acid has a much higher specific gravity than water - meaning it is heavier and will sink to the bottom of the container. It is highly miscible, so it will eventually mix in on its own, but I would give it a stir just to be sure.
I’ll give it a good shake.
Will it settle out over time?
No. Once its mixed it will stay that way. Its just right after that initial pouring in thats any concern - and its really not a big a deal. Most times you will likely get enough mixing action just by moving the jug around, handling it, etc, to thoroughly mix it, but its still a good idea to give it a stir or shake.
So I just used this diy ph down. In a 5 gal bucket of ph 7 water with mega crop nutes, it took about half a cup to bring it down to ph 6. The ph down is about 2. I’m not used to using that much to bring it down.
that seems like a lot, i usually only need to use smaller amounts, are you sure you use the right ratios?. Calculate how much that cost you compared to other ph down solutions to reach that level, see if you think it is worth it.
Look on one of the containers for a Specific Gravity number. It might be shown as S.G. or SG. On my box its is S.G. 1.265.
If they came in cardboard boxes, it might only be on the box and not on the plastic container. The number should be at least 1.265 or very close to that. If its less than that, it is diluted.
Also, the Mega Crop should have lowered the PH some before you ever put the acid in. Did it?
Finally, how much you need will vary depending on your water.
In my case, I usually fill my rez to between 6 and 8 gallons. It generally take about 20-30 ML to bring it down from 6.7 to 5.7 or so. Actually, adding nutes drops it down to 6.3-6.4, then the acid takes it the rest of the way.
I suspect your acid is diluted. The stuff I buy at my local auto parts runs about $8 for 1 quart here in Wa state, where are you? Its been more than 2 years since I bought my last quart so the cost may have gone up.
Edit:
I just checked my diluted acid mix and the PH 1.08
There is nothing really wrong with what you have, so dont get too worried about it. It just means you will need to use more each time you use it. No big deal. If you want to make it stronger, you could just add another cup or two of the acid.
On the other hand, having it more diluted means you are less likely to go too far. Having it too concentrated makes it more difficult to make small adjustments sometimes.
Mine is the same s.g. I’m in Minnesota also.
Mega crop doesn’t seem to Change the ph. I’ll probably just mix it a bit stronger next time.
I use sulfuric acid also with my well water that is solidly buffered between 7.1-7.4 depending on recent rain/snow or lack there of.
I use the battery acid straight and it takes 1.5 ml/gal to get my ph down to 6.0, I grow in coco btw.
That is solid data! 
Cheers
G
Awesome thread @monkeyman!
I got myself a jug of 98% sulfuric. I’m gonna water it down tomorrow and start using it.
I’ve noticed myself and read from other people that GH ph down leaves a bit of a slime residue, and I don’t like adding the extra P so this is
Thats that good 18M stuff!
Just remember to ad acid to water and not water to acid. Drop water into conc. H2SO4 and it will blow up in your face. Doesn’t actually explode but the water turns instantly into steam and it all blows out. Like spilling water into a deep fryer.
^^ Yes very important to remember. And concentrated sulfuric is very caustic, so acid resistant gloves, safety goggles and I wear my face shield as well. And do it outside where it’s well ventilated.
I’ve been using lactic acid 88% since I already have it on hand for home brewing. It doesn’t take much at all to get pH down. Does anyone see any issue with this?
this warning only applies to soil? phosphoric acid would be good ph down for hydro right?
Yes, but watch the strength.
Don’t try using the 80% directly, cut it to 20% first. It’s still a little ‘twitchy’ at 20%. It acts pretty quick but let it set for 24hrs (or stir) to settle.
I’m starting to suspect it might trigger potassium deficiencies.
Cheers
G
ive been thinking about this. I prepare my solution in 10L bottles with tap water and i was thinking i would just test with 1/2 ml or 1ml per 10L and stir/shake, and then put my fertilizer (i already know how much it further acidifies).
if I do this i wouldnt have to pre-dilute right? cus if youre saying i have to pre-dilute in RO, im fckd, cus I only have access to 120ppm tap
My problem has always been ph up… with some of my FPJ and FFJ it always gets a low ph. I had used bicarbonate of soda to up it!
