Wild pH swings when adding UP or DOWN solutions

9 years ago

I haven't had much experience w/hydro. I started out growing some lettuce to get a feel for it and now am trying to grow an outdoor tomato plant using a drip system in a 5 gal bucket.

In my experience with the lettuce I could put about 1 to 2 mL of DOWN into the 1 gal bucket I was using and would see a small change in pH i.e. ~7 down to ~5.5. After a week of having the tomato growing I checked the pH and it was high (7 - 7.5). I added 2mL of DOWN to 3 gal of solution and checked. It was below 4! So I added 1.5mL of UP. Now it was so high something in the solution had precipitated out giving the nutrient solution a cloudy appearance and the pH turned out to be >9 (never saw this in the smaller system even using 2 to 3mL of UP)! So I tried 1mL of DOWN and it was back below 4 again.

It never changed so much with such a small volume of acid or base in the smaller 1 gal bucket. Is it possible that the plant has just used all of the nutrients in this short time and the solution has lost its buffering ability? The plant was already about 3 ft tall when I transplanted it into the hydro setup. I don't have any way of testing the conductivity or TDS.

P.S. can you tell anything about the nutrient concentration by checking the specific gravity with a battery tester or something similar? How about ohm testing it with a multimeter?

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Comments (2)

Rio_Grande
9 years ago
If we are talking 5 gallon bucket quantities you need to be thinking drops insted of ML. Ph adjustment is like hunting, you have to sneak up on it. Slow and easy.

As for checking your solution, you can get an idea with an ec or ppm meter. I use ppm, but want to switch over to EC
grizzman
9 years ago
What was the pH when you initially mixed the nutrients?
Also, what is the pH of the water you're using before you add any concentrated nutrients?
Do you have any idea what concentration you were aiming for when you mixed it?
Tomatoes are heavy feeders. If they're in a vegetative growth cycle they may be consuming a lot of your nitrogen which will cause your pH to rise. I believe consuming phosphorus will do the same thing. But it may be potassium. I tend to get those two confused.
By the way, a swing from 7 down to 5.5 is actually a pretty large swing in pH. you have to remember those numbers are exponentially related.
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