PH and TDS are all over the place

I’m growing two Girl Scout Cookies in a hydroponic setup. It’s deep-water culture with a drip top feed. I’ve used this setup for my last two grows and it works great. Both plants look great but the pH and TDS are all over the place. One day pH is 6.0 24hours later it’s down to 4.8. TDS keeps climbing not adding any new nutrients since changing solution on Monday (it’s Thursday now). Every day when I check the plants it’s been the same. pH drops, TDS goes up. Any suggestions on how to get things to stabilize. Using General Hydroponics 3 part Flora system feeding at about 70% of what they recommend for light feeding.

I have ruined many plants. I was using “one” PH meter. Big mistake. Now I have three good PH meters and a package of test strips. After figuring out my problem , I found I was watering with 2.0 PH. My green thumb is back.

What is your target EC for full strength nutrient solution? GH’s light feed chart is for smaller containers and multiple feedings daily . . . not intended for continuous feed such as DWC.

What are your res/nutrient temps? How much water are they drinking daily? Any issue with roots?

Best guess would be that they aren’t feeding, resulting in salts buildup which will tank pH fast. Starve them for a day and see how they respond . . . flush with 5.8 water from the top to rinse media and roots; then fill res with just water (pH 5.8) for 24 hours. Change res, add nutrients at ¼ strength. EC should drop by as much as 50% the next 24-48 hours to indicate they are feeding again and pH should begin to stabilize around 5.8-60.

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Thanks. I just finished replacing the water I put in yesterday. Used 25% of what the General Hydro chart shows for a light feed. I had a bad case of nutrient burn on my last grow right at the end. Had to harvest about a week sooner than I wanted, but still had a decent yield and potency. Don’t want a repeat with this grow. I’ll update again later in the week.

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The flush was just what they needed. After a change of solution pH has stabilized at 6.3 and TDS is dropping from 840 where it started. Both plants look great and one has flipped to flower

Thanks for the suggestion.


I have a pair of Grape Apes I was having the same problem with but your solution fixed the problem and everything happened exactly the way you said it would. They are looking good and feeding again.

Thanks for posting your solution.

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