Weird ppm/pH problem: fast ppm increase, as well as pH

Hello everyone,

Perhaps someone could shed some light into my problem. I have a DWC system with one plant in it (rock wool + hydroton). The nutrients I'm using is Hesi Hydro Grow. When I set up the system, I used tap water (ppm = 240, pH ~ 8 + 50% the amount of nutes indicated on the nutrient bottle label. After the mixing was done, the total ppm = 360 for the water + nute solution was around 310, ph ~ 7. After adding acid, the final pH of the nutrients solution was around 5.8 and ppm=326. The rez has a volume of about 30L (about 7-8 gal). The solution was clear.

About 24h later, when I checked the ppm and pH, it had a pH of 8.1 and ppm of 394. Also, noticed that it turned milky and has a damp smell to it. For this particular solution, initially, I used vinegar to lower the pH. vinegar is a very weak acid, so i decided to re-balance the pH using a much stronger suluric acid, This morning I rebalanced the pH with sulfuric acid to a pH of 5,8.

10 hours later, when I recheck the nutrient solution, it has a ph of 7 and 500 ppm. As you can see the pH and solids concentration keep on increasing. So now, I diluted the nutrient solution and rebalanced its pH to 447 ppm and pH 5.5. Additionally, I added 3% H2O2 thinking that maybe the smell is coming from some mold forming somewhere.

Also, I set up nutrient solution in 2 test containers hoping that I can reproduce the behavior. One of the containers has water + nutrients + sulfuric acid and the other one has water + nutes + vinegar + acetic acid.

If anyone has any ideas, I'm open to suggestions. I plan on cleaning up the tank and re-mixing the solution using either phosphoric acid or nitric acid as ph regulator tomorrow.

Thanks guys and girls

I have two ideas. The number of right ones could be two, or zero, or something in between.

When you mixed nutes into 240 ppm water, you generated a fair bit of carbonic acid. I've witnessed pHed mixes in 70ppm water rise a full unit on standing.

The other thing I had was a batch of nute to which I'd added Superthrive. It started at 5.6 and went slowly down to 4.38 (!) as it went cloudy with bacteria. Once the bacteria died, the pH slowly returned to 5.7 ...
... my advice is to not use an organic acid. It feeds bacteria, which will upset the ion balance, notably pH, of your nutrient.

When you clean your res, disinfect as well. i suspect bacteria contributed to the issue.
The other thing is, give your nute a good blowing with an airstone. It'll accelerate the pH rebound, after which you can pH down to a stable value.

I don't know why your ppm are rising like that.
Is the Hesi a "one-bottle solution"? You might want to try nutes for your high ppm from the tap, e.g. GH Flora 3-part for hard water. cn

Thanks for the input.

Carbonic acid would explain the initial increase of pH and I doubt it would amount to nearly 3 points. Carbonic acid is also very unstable and dissociates quickly into water and CO2.

I also thought about bacteria as the origin of the smell and I spent some quality time researching their effects. Apparently they lower the pH, so I would expect a progressive decrease of the pH should bacteria be involved.

Currently, my hypothesis is that the nutrients are reacting with the acid using it up and causing some sort of precipitate which would explain the pH increase. However I don't know what effect it would have on the ppm.

I'll clean up the rezervoir tomorrow and wash it real well and then use only an inorganic acid to balance the pH, see what gives. If the result is the same, I'll get the nutrients you recommended.

Another thing I'm wondering about is whether the air stones don't react with the nutrients/acid. I have 3 of them and are bubbling really nicely. The nutrient looks as if it's boiling.

I stopped having pH problems right after i stopped checking it. lol

faller200 said:

I stopped having pH problems right after i stopped checking it. lol

Click to expand...

haha, well me neither

An update: Since I cleaned the rez, replaced the nutrients and since I used only inorganic acid to balance the pH, the problem seems to be fixed. I don't see any drastic changes in pH, nor in solids concentration. I'll keep on monitoring the grow and trying to resuscitate the plants which went from happy campers to grumpy in no time.

Thanks guys for the input.

79531 said:

An update: Since I cleaned the rez, replaced the nutrients and since I used only inorganic acid to balance the pH, the problem seems to be fixed. I don't see any drastic changes in pH, nor in solids concentration. I'll keep on monitoring the grow and trying to resuscitate the plants which went from happy campers to grumpy in no time.

Thanks guys for the input.

Click to expand...

just a word of caution the combination of nearly anything you would normally put in your res coming in contact with sulfuric acid is not a good idea. per the msds of sulfuric acid all organic things react violently with it it is very bad for your roots and plant as a whole as well as being a known carcinogen when inhaled( or smoked) it reacts violently with phosphorus, h202(peroxide) nitric acid, potach, dolemite, acrylates(moisture control beads) organic acids are actually one of the best things for your grow gh uses citric acid as a buffer along with phosphoric acid. organic apple cider vinegar has the added benefit of killing off anaerobic bacteria which can further be enhanced with an airstone. the acetobacter in acv will help break down nutes especially from compost teas and respond well to hydrogen peroxide without having the negatives of sulfuric acid. the problem wasnt the type of acid you used as organic and inorganic is used in commercial ph downs, but the sanitation of your res. it was either not enough oxygen, a reaction from sulfuric acid, or excessively hard water. very hard water is considered anything over 180 ppm, your tap water was at 240 or 25% harder than very hard water i think that is your problem. alot of times people go with a very strong acid without thinking about the reason they need it in the first place. i also think the hardness of you water created an environment that was basic enough for bacteria to thrive. a strong acid might patch your problem now but it will come back based on your water hardness. the solution is a reverse osmosis filter. sounds expensive right? well you can make one from a mr clean spotless carwash. buy the starter kit it can be had from 20 to 12$ and the replacement filters will last 3 fold. its really easy to make and it will bring your ppm from 6.4 to 8. dont settle for a brita filter the filters are expensive and they affect the taste not the ppm as they are made of carbon.