RDWC Ph is dropping half way through flowering....fast

Ok so… 200 gallon rdwc. Plants appear to be doing ok. roots look good. water temp is 68. system gets @30 gallons of fresh RO water every day, with 1/4 strength nutes… ppm(500 scale) 400. I will get the ph to 5.8-5.9 and the next day it is 5.0. been doing this for at least a week… any ideas? what causes the ph to drop?

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Bump up the solution concentration which will hold it at PH longer. Also salt exchanges between roots and rez can affect PH. Make sure of root health as dead plant material will acidify the solution.


gotcha… I had some fungus gnats try to move in but I evicted them promptly… some larva could have gotten to a few roots but i don’t see any sign yet. I use hydroguard also, so hopefully, that takes care of any dead roots! ? I guess with ph dropping it could mean i need more hydroguard?


What’s the rez temp? Under 70F?

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yeah, 68 but i have had problems before under 70 so i just always use the hydroguard… sometimes I’ll run sterile with hypochlorous acid until I end up needing the hydroguard… Do fungus gnats have anything to do with PM? like do they spread it or make it worse? have it on their feet?

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Insects would be a vector of transmission for sure.

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ok… so when I spray the PM with h202 & RO water, does the PM disappear, or could it still look whiteish but dead? So like if I douse the plants in h202 then see the PM the next day… is that new stuff, dead old stuff, or did the spray just not take it out? Does the browning of the white hairs make the buds finisher quicker or does it just turn them a different color?

This is what I found: it disappeared within seconds. One side-effect is it can burn the pistils. I hammered mine hard with several applications then only as needed. That allows the plant time to put out fresh pistils (which it should do continuously throughout flower).

ok so if i see more then I didn’t spray it good or it is new. So I should make it rain h202 & RO water a few times… consecutive days, then spot spray.

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Make sure you increase airflow too to reduce it recurring. Might want to invest in a dehumidifier at some point too. I had to in Southern California.

ok, yeah… The dehumidifiers I have and using can extract 98 gallons of water from the air per day. I need to use a biocide fogger bomb thingy between crops, shouldn’t I? It keeps coming back with the humidity at the perfect VPN…40-50% daytime78 degrees / 30-35% night…67 degrees???

Hey! on the h2o2 spray… are we talking about the 3% stuff or the 30% food-grade stuff? Mix 3ml/gallon of RO water?

3% is what you want. 30% is closer to rocket fuel.

yeah, it lets you know if you get any on your skin! So, 3ml per gallon is the correct amount?

Per quart. If not effective you can keep increasing strength up to 50/50. Stronger solutions will have a drying effect on edges of leaves and pistils FYI.