Need advice on runoff numbers

My Girl Scout Cookies Extreme autoflowering is at 29 days above soil. I watered this morning to runoff for the first time.

My PH in hovers around 6.5 to 6.8. The runoff tested at 5.6.

My TDS tested at 1227 ppm.

I measured approximately .25L of runoff water in the tray. .25 as in 1/4 of a liter.

I am not using any nutrients yet and am in Fox Farm Ocean Forest soil with about 25% added perlite.

Why is my runoff PH low and how do I fix that? Are my ppm’s too high?

Is it possible that the plastic saucer I am using is affecting the readings?

The leaves are a little droopy in the pictures because I let the soil dry out quite a bit before watering this morning. Usually they are reaching upward toward the light. I am not seeing any leaf issues. They are all green and shiny. Thanks.


I rinse my trays between waterings. The salt buildup will otherwise corrupt your pH and PPM readings. PPM is fine. pH of 5.6 is too low. Check it again after your saucers are clean and if still low you can use something like this.


TDS numbers seem kinda low for Ocean Forest. You might want to double check your runoff. Plant looks good though. The PH out is a bit low but not bad.


I do have that exact brand of PH up and down. The tray is brand new with no salt buildup since this was my first time watering to runoff. Just to clarify, you saw that my water PH in is around 6.5 to 6.8? Thanks.

Yes, but runoff is the best measure of what is going on in your soil.

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If my TDS is low does that indicate it is time to start using nutrients. I have the Fox Farm Trio but haven’t used any yet. Thanks.

So are you saying if my runoff continues to test low I should increase the PH of the water in higher than it is currently?

Fresh OF runoff should be north of 2,000 ppm and closer to 3,000 based on others. I’d recheck. You should not have to feed until flower.


Yes. I’d probably put in water pHed to 7.3 for a few waterings to slowly bring it back up. It’ll be really important when you get her to flower when the ideal pH should be around 6.5.

I’m kind of surprised that OF is creeping low on you given that you’ve not given nutes yet. OF is pH buffered pretty well. Have you checked the calibration on your meter?


I already dumped the runoff but tested it multiple times. If it makes any difference my PPM in the tap water is very low, around 45.

I calibrate every time I use my PH meter in the 4.0 and 7.0 solutions and it is right on.

Could I be getting a low reading because I have been watering in small amounts so far? Some sort of buildup that needs to be flushed perhaps?

It’s impossible to properly pH water with a PPM that low. If you find it necessary to raise pH, then I’d add something fairly neutral like a tbsp of epsom salt or a ml or 2 of cal/mag to give the pH Up ions something to grab hold of. If you have the FF Trio then a ml of Big Bloom would be good for that too.


You won’t have a buildup if you haven’t been feeding.


Thanks guys. I will try adding the big bloom next time I water. I will continue to monitor and check back in if problems arise.

Don’t forget to pH adjust last, after you’ve added whatever you are going to add.


@TheAccused here is the post with the full pics of my plant that apparently started flowering today!

Yea, u shld have already been feeding her I’d say, but dont worry man, she looks fine

I get lot’s of conflicting advice. Most people said to wait 4 to 6 weeks before adding any nutrients. I’m not sure how many of them realize I’m growing an auto even though I specifically say that in my post.

Yea, I get conflicting advice on here sometimes too, but theres like a million ways to grow these plants and no 2 growers do things exactly the same, two things I can tell u for sure is listen to what ur plants r telling you n dont get stressed out, these plants r tougher than u cld imagine…n I started giving mine nutes after the first cpl sets of leaves came in but I use different nutes than you, on mine it’s got dosages for seedlings/cuttings, small plants and also mature plants, I also found that I wasnt watering mine enough at first

I did an experiment and filled a watering can with tap water and measured the PH. It was previously testing right around 6.5 to 6.8. Now it is testing at closer to 7.3. I guess tap water has the potential to fluctuate depending on how the city treats it and as you said it is impossible to PH water with a low PPM.

I then added some of the grow big and tested the PH again. It now read 6.4 to 6.5. My question is this: Do nutrients typically lower the PH or am I just getting a “real” PH reading now that I have added something to raise the PPM? Thanks.