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Coco/Perlite - PH Runoff Far Too Low / Cant Raise It

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    HELP! Coco/Perlite - PH Runoff Far Too Low / Cant Raise It

    Hi All,

    I am at a bit of a loss and hoping that someone can help me. I have been growing indoors for about a year now and ive had two very successful harvests but have been struggling with all my plants since then. I am top feeding my plants.

    My Setup:
    I have about 5 plants in one tent under t5 lights and 3 plants in another tent under 1200W dimmable COB LED's(These are my flower lights but keeping these plants in VEG until i can find a solution to this problem) All of my plants seem to be affected.
    • Clones or Seed?: All plants are clones from a mother plant which recently died due to a completely unrelated mistake.
    • Strains: Half are Critical Kush and others are Fruity Chronic Juice
    • Pots: Smart Pots (Fabric Air Pots)
    • Nutes: GreenHouse Feeding Powder feed all-in-one Veg nutes with calcium added. (I add 50PPM calc to every nute batch) LINK!
    • Grow Medium: COCO and Perlite only. ~70% COCO and ~30% Perlite.
    • Lights: Veg with HO t5's (6800K) and flower with 1200W COB LED's
    • Grow Space: Inside a grow tent with full extraction setup and oscillating fans.
    • Pot Size: Some in 5Litres, some in 10Litres and some in 20Litres as they age. (ALL of them are affected)
    • Tap Water: Comes out at around 8PH and ~90PPM (Its potable water)
    • Measuring tools: I have a relatively expensive and new PH pen metre and a PPM metre with thermometer built in.
    • Training: Plants are low stress trained to have a flat canopy and only few bud sites (usually about 3 or 4 buds per plant). I pick off new bud site growth.
    • Feeding Schedule: I usually water once every 3 days depending on how dry the pots feel. Bigger pots take longer to dry. I normally water until i get about 30% runoff but i may have been overdoing it recently.

    Problem Description:
    The runoff from my plants is around 4.5PH with some even lower than this.
    I used to water my plants with 5.5PH and i had good success with this until i noticed that the runoff PH was dropping too low on my recent plants and they were starting to get affected with slow growth and yellowing of the new growth.
    I started watering with 6.5PH and now im watering with 7PH in desperation but when i test the runoff its still around 4.5PH...

    Click image for larger version

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    Two of my plants look WAY worse than the above. I just havent got a photo of them right now.

    What i have tried:

    The first thing i tried(BEFORE i checked the runoff PH) was to add Epsom Salts to the nutes because i first thought it might be a magnesium deficiency. I added epsom salts for a while and but the plants started getting worse so about two weeks ago i stopped. They now look terrible.

    So recently I have been trying to flush my plants with higher PH water in an attempt to bring the runoff PH back up. But this seems to make it worse??
    With two of my 10L pots i flushed the coco with water straight from the tap(~8PH) and i flushed them with probably 4 times+ the volume of the pot, i then tested the runoff and it was about 5.4PH after starting with about 4.4PH.. This was still too low but i flushed the living day lights out of these pots trying to bring the ph up and then gave them a slightly lowered nute solution at around 7PH but obviously this hasnt worked at all and then the next day they look way worse! And at the next watering i measured the runoff again and it was even lower than before..

    My Theory:
    So after seeing that the plants i flushed looked even worse than before, i realized that flushing may be making it worse?
    I now believe that i may have been watering my plants too much to begin with which could have caused the PH to start getting lower and then when i noticed the signs of low PH i attempted to flush the plants thinking this would help but maybe this is actually the cause of the problem??
    Reason i thought that i might be watering too much is because i was giving the 5L pots only 1litre of nutes for a while whilst i was giving the 10L much more and the 10L looked really bad and the 5L looked good. Now almost all of my plants look bad after flushing and watering a lot.

    If anyone has encountered this problem before please help me. Nothing that i have tried is bringing the runoff PH up at all, no matter what PH goes in the top.

    I read that low PH in the run off can be caused by salt build up so I did a flush with Florakleen to get rid of the excess salt and the PH in the runoff went up. I think washing out any salt build up is the reason most nutrient suppliers recommend 10-30% run off. Also since it is hydro I dont think its a good idea to let the coco/perlite mix dry out. Your plants look pretty good though


      Have you calibrated your pH pen lately?
      Yo mama was a snowblower.


        How often were you watering? I had a low pH for a while when I was watering every 36 hours. I hadn't had this problem in previous grows, and I was watering once a day with those grows.

        I figured it was a salt build up and gave them slightly less nutes at a pH of 6.4ish (I normally stay at 6.0). It seemed to fix the problem.

        Hope ya figure out how to fix it!

        Past Grows


          Thanks for responding guys.

          Allenpro , I also read that and thats why i first tried flushing them. But i think my mistake was flushing them too often..
          Unfortunately i havent found a place to get florakleen or clearex where i live.. does any know of an alternative i could try?

          Mr.furley , not yet but i recently got calibration fluid and intend on doing it soon. But I have tested my ph metre against a friends which is also of good quality. I have a liquid test kit as well that ive compared to and my tap water is a pretty consistent number here at 8ph and I've compared that as well. So im pretty sure of the ph.

          Doubledealing72, i was watering probably once every 3 days for most of the plants.. thats when they usually needed to be watered. They didnt dry out completely between waterings.

          So what i did yesterday was feed them with 100ppm less than what i was giving them and ph'd the water to 7ph. I only watered them enough to see water come out the base of the pot.

          They still look crap today.. im just hoping they come around maybe after the next watering? If they dont then im i have no idea what to try next..


            Hello ,Is it possible to take a couple of pictures of your bad looking plants ?
            Cfls for a week or two
            315lec for everything else
            Dug up Ms.topsoil, with perlite added
            36x36x63 inch tent.
            6inch - exaust - intake fans an scrubber
            Smart pots


              Originally posted by D.A.A.S.69 View Post
              Hello ,Is it possible to take a couple of pictures of your bad looking plants ?
              I will take a picture tonight.
              I have like 2 plants that are still alright and 2 that i should probably just throw out at this point because they look so bad.. Im hoping i can figure out the problem though, so im keeping all plants for now as experiments.(Dont want this to happen for any future plants)


                Your Leaf looks dark green in the pictures, any chance you've given them too much nitrogen? I too would like to see the plants.
                Yo mama was a snowblower.


                  Will get more pics when im able to later on. But i can tell you with 100% confidence that i have not overfed any of these plants. Only possibility is that maybe a specific nutrient is getting trapped in the coco and flushing with water is not getting rid of it? And its causing the ph to drop? Im pretty sure low ph in the pot is the cause of these problems but i dont know what the cause of the low ph is...

                  Im also using all-in-one powder nutrients so its not easy to give too much of one specific nutrient.

                  I have had two successful harvests before this batch of plants. And i fed the previous plants far more than i am now. I've been keeping the ppm low in my attempts to get them to recover.

                  The dark leaf may be caused by my LED lights over that particular plant. The ones under the t5's are not as dark but have the same issue.

                  My biggest question is how the PH managed to drop so low in the pot and also how can i effectively raise it? (seeing as though high PH flushing appeared to make it worse) when i tested the runoff from each plant, the ones that looked the worst had the lowest ph runoff.


                  • D.A.A.S.69
                    D.A.A.S.69 commented
                    Editing a comment
                    In coco, you will be chasing ph runoff forever, it's almost impossible to flush coco, to get your ph right.

                  • Mr.furley
                    Mr.furley commented
                    Editing a comment
                    It says you add calcium is there not magnesium included? Have you used your TDS meter to see what your PPM, your runoff?
                    Low ph is caused by salt buildup from overfeeding, poor watering practices or not flushing your Coco properly. If it's PH then it one if not all of them
                    I think you need to let your pots dry out a little long in between watering, if you are feeding every water maybe think about adding a water only every other time. I'd start there. Maybe give her another flush.
                    Last edited by Mr.furley; 11-20-2018, 10:09 AM.

                  Holy crap you need some of my PH 8+ tap water. I have the opposite problem.


                    Sorry for taking long to respond.. hectic week.

                    Im definitely not gonna try flushing them again. I have overdone it with the flushing and yes i have tested the runoff ppm a few times. The first time i tested was before the issues were this bad and the runoff ppm was a a few hundred ppm higher than the water going in. After all the flushing with tap water i got the runoff to the same as my tap water and then flush-fed them with lowered nutes straight after the tap water flush.

                    My nutes do have magnesium in them but not calcium because some tap water already has enough calcium so they sell that as an extra incase you need it.

                    I have attached two pics of one of my plants. I sincerely apologise to all weed lovers for the disgusting state of this plant. I know it hurts to look at but you guys asked for it.
                    Attached Files
                    Last edited by SiriusBisness; 11-21-2018, 09:46 AM.


                      So ive been trying to think back to what happened when my plants first started showing these symptoms..

                      I remember with one plant in particular it was looking really good still whilst the others had already taken a turn for the worse. I fed the good plant with some nutes that was left over from watering another plant(a plant with bad symptoms) and then the next day it was showing bad symptoms like the others and i fed it normally, didnt flush it but didnt under water it.
                      The good looking plant was being fed from a different container before this particular watering.. Maybe theres some sort of bacteria/algae that might be in my mixing tubs??

                      Im thinking algae can cause this because i know algae can drop the PH of a reservoir of water in DWC systems and can also potentially cause the plant to starve as it fights for nutes. The only problem with this theory is that the water in my mixing tubs does not drop PH over night or even after 2 - 3 days. In fact i just tested one of my tubs of nutes that was mixed 2 days ago and the ph actually went up by 0.60PH.

                      So maybe there is algae in my soil? Affecting every single one of my plants? I seriously dont know.. i never had this issue before but im pulling my hair out over it now.

                      Either that or a disease has spread across my plants? Or my tap water has just straight up become poisonous now... -_-

                      Im making sure that the pots are dry before i water them now too.
                      They dont look any better after the last watering of 7PH and i only gave them just enough to see a little water come out the bottom. I have double checked my PH and PPM metre.


                      • Mr.furley
                        Mr.furley commented
                        Editing a comment
                        Sounds like you're covering all the bases, couple things to mention moving forward, it looks like your pots are sitting on the ground getting some air flow up underneath them by elevating them would be a good idea if you don't do it already, two is letting your pots dry out till they're Featherlite will take care of any algae that you may have accumulated in the soil by leaving them wet all the time.

                        I would also suggest to add some calcium as calcium and magnesium need each other to absorb your symptoms are looking like calcium deficiency. I don't trust tap water to give me the calcium levels my cannabis needs. Cannabis best absorb calcium and magnesium at 6.2 6.3 range in coco.

                        Lastly I would suggest to mix your newts for your watering and discard extra if any. don't store them for later use.

                        Good luck and keep us posted.

                      What kind of Coco are you using, some coco is heavily amended, like Coco-Loco, from FoxFarms, that's the kind of Coco I use, when I'm using coco.
                      But I strickly grow in living soil now, to much work involved in coco, for an old man like me anyway.
                      Plus I never saw any faster growth using coco, anyway, even by feeding 2-3 times a day, all i saw was more work,lol
                      But some folks love coco, just not me.
                      Cfls for a week or two
                      315lec for everything else
                      Dug up Ms.topsoil, with perlite added
                      36x36x63 inch tent.
                      6inch - exaust - intake fans an scrubber
                      Smart pots


                        Thanks a lot for the suggestions guys! Its much appreciated.

                        I have taken all your advice into consideration.

                        I do add calcium to my nutes(same nutrient brand as linked in the first post). I add 50ppm calc to every batch. This has worked perfectly for me in the past so i guess theres no problem here.
                        • I have let all my plants dry out completely before giving the smaller ones another water with 7ph 2 days ago.
                        • I gave one 10L plant just tap water yesterday as a test. Left ph at what it comes out as 8ph.
                        • I put h202 into the nutes for 3 of my plants as a test. A few mls of 3% h202 into the nutes.
                        • Cant remember brand name but its advertised as "super washed coco" and prebuffered. It was a lot more stringy than my last batch though..

                        Nothing. Changed. They still look terrible..

                        I dont think its my coco because these plants were thriving and some of them were pretty big before they all got trashed by a some unknown force.

                        Weirdly though one of my plants under the LED has almost completely recovered(it looked terrible before with the others.) It hasnt been watered for about 7 days now and is almost feather lite. But i have not done anything different with this plant and two other plants next to it look horrid right now..

                        I am so confused.

                        Is it possible for my nutes to go bad? I put them into airtight clear plastic containers. Is it bad that light can get to the nutes? Its powdered nutes.
                        Last edited by SiriusBisness; 11-27-2018, 03:45 PM.


                        • SiriusBisness
                          SiriusBisness commented
                          Editing a comment
                          Also; Does anyone have any suggestions on what i must feed the one plant that's almost recovered??

                          I dont want it to get messed up again like the others and im scared that its gonna start dying right after the next watering like the others did..

                          So any suggestions for the PH and nute strength i should use? Bearing in mind that my runoff has historically been around 4ph - 4.5ph and i would usually have been feeding this plant around 900PPM cause its relatively big.

                        • Mr.furley
                          Mr.furley commented
                          Editing a comment
                          SiriusBisness , the one that looks to be recovering, what size pot is it in?

                          When was the last
                          Nute feed?
                          Water only?

                        Hi everyone.

                        Sorry i didnt get back to those who tried to help. I just wanted to post here again to let everyone know how i solved this issue in case someone finds this thread and has the same problem.

                        It was my veg nutes! I followed the process of elimination and just kept changing one thing at a time until the plants started to look better.

                        The last thing i changed was my veg nutes.
                        I had a tub of random nutrients that i got from the nursery(These nutrients are not made for cannabis they are just all purpose nutes for random house and garden plants) and decided to use them as a test. The plants started recovering almost immediately.

                        Now i still dont know for certain what happened to my Green House Seeds veg nutes but my theory is that moisture got into the tub they were stored in and messed them up somehow.. They were stored in a 4 clip seal airtight plastic container but i did notice that some of the powder was sticking to the sides of the tub.

                        All of my plants are now looking amazing and from now on im going to keep those de-humidifying silica bags in my nutes.

                        Has anyone here ever had a batch of powdered nutes go off like this?


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