Drainage ph falling


first grow … growing in ProMix organic microactive … 18 days into flower … drainage ph was about 6.3 but with each feeding it has dropped … first to 5.9 then 5.8 and now 5.68 am using general hydroponics 3 part flora mix,
cal-mag, molasses, Epsom salts and Advanced Nutrients Big Bud bloom booster … using tap water at 5.9 … drainage ppm about 825 any help appreciated

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Your tap is 5.9 or your nutrient solution is 5.9 after being mixed? Chances are your nutrients lower ph a little, you can/should adjust this before applying.

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tap is about 7 … adjust ph to 5.9 after all nutrients have been added


Given you are using moleasses in the mix your soil microbes could be eating and lowering the pH. You do not want to overwater when using sugars as anerobic bacterial growth will be favored. The anaerobes do not efficiently break down sugar and can create acid biproducts instead. Think of vinegar production.

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have waited until soil is dry and pot is very light to water plants …i feed every 3 or 4 days … have used molasses from start of grow and ph was fairly stable …I calibrate my ph meter with buffer solution every week … problem started when I increased nutrients for flowering , i try to increase nutrients slowly and am almost at full strength … i flushed plants about 18 days ago until i had 70 ppm in drainage … at what ph will this become an issue … plants look good now but am afraid this will hurt them …. thanks for the reply


Tap water has very little buffering capacity. Your base nutes if pH’d properly should hold the pH in the soil. BTW plants cannot absorb sugars directly through the roots. They need to be acted upon by microorganisms in the soil. It is your nutrients that provide for plant growth.


this is my first grow and i am following grow videos by nv closet med grower that were on you tube… watched vids and made a pile of notes and am trying to follow what he did … all seemed good until about 2 weeks ago … made notes on what i was doing and problem seems to have started when i increased nutes and added Big Bud … maybe just coincidence … thanks i appreciate info

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After adding nutrients, you could consider pH’ing to 6.3 for the time being, and monitor the runoff to see if it starts to rise. Any symptoms showing up on the leaves?

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Seeing a PH drop in flower is pretty common and some of it has to do with the root volume the plant is occupying. If all of the available space has been taken up (and boy do you get roots with cannabis!) the media can’t really buffer the waste salts being exhausted from the plant so you see a drop in PH. It may get pretty advanced just before harvest. @Not2SureYet had this on a coco grow some time back.

Nothing more to do than what you are doing although I might try to keep my input around 6.0: that seems to be a sweet spot for a lot of media growers.


I will ask what you tap water ppm is at the start. Any thing over 200 and you will want to use hard water micro. And for me in coco. The heavier I feed. The faster my ph will drop too. Try feeding at 1/2 that for a few times and I would bet your numbers will drop again. If your plants are happy. I would just watch for issues and address them at that time. My numbers tend to float a lot too. I rarely have any issues from that.


tap water ppm is less than 40 most times …plants look good – to my eye… had some small brown tips on edges and tips of 3 older fan leaves but haven’t found any more … the issue is occurring with 2 pineapple express plants , both the same age … plants are each in a 4 gallon plastic pot and I use 1&1/2 to 1&3/4 (us) gallon of mix each feeding with 1 to 1 1/2 quart drainage … will keep nutrient mix at 6.0 or higher and watch the see if ph continues to fall … would a flush help?
have some pics taken today … plant 1in pic 1&2 …plant 2 in pic 3&4
thanks for the responses , all info appreciated


I wouldn’t flush until your plants show symptoms. Yours look nice. You are using a near soil-less medium - predominately peat moss, coco, and perlite - and 5.6 isn’t out of the pH range of soil-less yet. I’d just be hitting it with 6.2-6.3 pH and see if it rises toward 5.8-6.


thanks for the advice sixpackdad
will raise my ph for the next feeding in 2 or 3 days time and hold off on a flush… what low ph would be a concern …

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Here are two charts, one for hydro/soil-less and one for soil. For soil-less you don’t want to be below 5.5. My roots organics soil-less medium is similar to yours - it’s got a little of the “soil” in it like worm castings and other organic nutrients, but it’s mostly perlite, coco, and peat moss. Their website recommends keeping it between 5.8 and 6.3 for example.



thanks for the charts sixpackdad … will update post after next feeding …
thanks to everyone for the help and advice


did feeding on one plant today and got these results … nutrient mix was
7 liters (1&3/4 gal) and ph was 6.2 with tds at 802 ppm … drainage was about 2 liters and I tested in 2 parts … first liter was ph 5.72 and ppm 935
then I emptied the pan and last liter was ph 5.85 and ppm 1197 … am I testing the drainage the right way ? any tips on the proper way to test drainage ?


Doing good! Generally the last 10% is retained for testing. I don’t see anything wrong with what you did.

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have numbers headed the right way and that is a relief … will continue with ph 6.2 for nutrient mix and watch the numbers … thanks for info on testing … lots of info on the web but I am not sure all is good …

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