Bad pH drop in coco...... what could be the culprit???

I have 3 Pure AK's that have been kicking serious ass for 10 weeks in veg. Until this week.... I am growing in 50/50 coco and perlite. I pre loaded the coco with 350ppm CalMag after hydrating and flushing the coco to get any possible salts out. They are under 24/7 T5 light in their veg cabinet. Temps are maintained @ 82-86F. RH is a bitch to maintain in my climate and is usually 16-20%. I overcome some of this by misting them 3-4 times a day with straight RO/DI water pHed to 6.5. They are watered/fed every 2 to 3 days depending on the how heavy the container feels.

Feeding Regiment: Water, staple nutrient then supplemental feeding. Wash, rinse and repeat. The cycle runs just about 10 days most of the time.
Water: RO/DI treated with 350ppm CalMag, 1 drop Super Thrive and pHed to 6.0-6.2
Staple Feeding: General Hydro 3 part mixed at 1/1/0.5 (micro/grow/bloom) in RO/DI pHed to 5.6-5.8. PPM's come in at 525-550.
Supplemental Feeding: 1tsp Alaska fish fertilizer & 1tsp Bio-Weed in a gallon of RO/DI pHed 5.8-6.0

For the feeding and supplemental feeding I use an amount of liquid equal to the size of the plants container and for the CalMag watering they get two times the volume of the container.

Just in the last week I have been noticing tip burn and burning along the margins of the leave as well as canoeing leaves (bent up). At first I was checking the pH of all of the runoff every time. But after 6 weeks of steady number I decided to forgo this because things look dialed in. Fantastic growth. Nice emerald green leaves. Responding very well to LST, FIMing and super cropping. After seeing the issue I shot a pH of my runoff with RO/DI water pHed to 6.0 and my runoff came out a 5!!! So by my figures the pH in my root zone is around a 4....

They have all since been on a weeks "bread and water".... well just RO/DI water pHed to 5.8 and they have perked up and the leaves are going back to a healthy shape. My question is WTF dropped my pH through the floor??? My speculation is that it is the fish fertilizer. Because when I add it to my RO/DI water it slams my pH down to the low 4's and it takes a good amount of buffer to bring it back up into range. Could my buffer be wearing off and letting the fish fert revert back to it's lower pH?? Has anybody else had this issue with fish fertilizer in coco.... or just in coco with anything?? Could I possibly help remedy this by adding in an additional watering day between the Staple and Supplemental feedings with just straight pHed RO/DI water to act as a flush?? Or might it be better to add some sort of buffer like dolomite lime and crushed oyster shell.

Thanks....

I sincerely appreciate the specifics, but that is was quite the read. I think you'd get more help if you made it a little easier to read. I'm the worst at this, I always end up editing the shit out of my threads.

Anyways, coco is basically hydro, and I know when you are growing hydro, mixing synthetics and organics can sometimes be risky business. Ca/Mg can often cause pH to drop way off, the pH of most synthetic Ca/Mg is 4.0, sound familiar? Are you using an organic or synthetic Ca/Mg buffer? Mixing is always dangerous, but I've seen a few gardens die over night from mixing synthetic base and an organic Ca/Mg buffer.

And when you are mixing synthetics and organics, a plain water feeding is a very good idea inbetween your supplement and staple feedings. I don't have any advice to raise your pH though, I've never had to drastically raise my pH, only drastically drop my pH before.

Sorry, I was attempting to paint as clear a picture as possible of the situation. Seen so many "Help Me" threads where they don't present enough information to give the more knowledgeable people on here enough to work with in order to help them.

I forgot to add that one of the main reasons why I am singling out the fish fertilizer is because this issue is only presenting in my vegetative plants. Not in my flowering plants which receive no fish fertilizer. The only "organics" they get is a tsp/gal horticultural molasses with their supplemental feeding.

When in doubt flush it out 100ppm A, 100ppm B, 100 ppm cal mag @ 5.8ph. Soil Borne pests (Fungus Gnats, root aphids) can cause rapid instability in PH. My guess is root zone decay that causes lower nutrient threshold and then burns. Don't start with lime and buffers. Start with a flush a, misting is a darkness activity and 4x day is way too much. Pictures.

Haven't seen a single fungus gnat. But maybe a prophylactic Neem treatment wouldn't hurt.

WyoGrow said:

Haven't seen a single fungus gnat. But maybe a prophylactic Neem treatment wouldn't hurt.

Click to expand...

The fungus gnat larvae is the damaging part....it lives in the coco....you will need a larvicide to get them right. Neem is always welcome. I use a sprayer with with neem, peppermint vegetable soap, cinnamon, baking soda, chili extract, and garlic powder and spray the bottom 1/4 of the plant after watering as well as any surfaces nearby and of course the coco surface. This is a great repellant to a large number of garden pests....my insurance policy. Look at Root Conditioners like Zone from Dutch Masters. They just sterilize and give the roots time to heal, the downside is that they kill beneficial bacteria too. I would flush and end with adding something like this. Hydrogen Peroxide also works for root funk....cheaper but has limitations that Zone does not.

Root funk could definitely be a problem. Pick up a pot and smell the bottom of it, see if you can smell anything pooey from the drainage holes. Not a sure fire way to tell, but you can usually smell the funk.

If you're afraid of the fish fert, I would definitely omit it. If you were to add it back I would just use that and molasses in between normal feedings and flushing.

OK... another odd thing is that it seems to only be affecting my Pure AK's. My Haze and Bubblegun look just fine.

Might I be experiencing a finicky strain exhibiting symptoms to a situation that the other two are more tolerant to?? They all get fed exactly the same.

Firstly runoff pH in coco is indicative of nothing. Its an ineffective way to test rootzone pH

There are articles on how to test rootzone pH posted around the net.

It involves distilled water and a coco sample being stewed for a period of time. Then strained and the remaining liquid tested for pH.


Have you been testing your runoff ppm?

Get 20% runoff out of your pots and test it for ppm.

If this is higher than your feed ppm you could have been feeding a little hard.



J

Coco,is the culprit

jondamon, thanks for the reply. There is so much contradictory information on the net it hard to know what advice to follow. I haven't been checking the runoff ppm. But I will now.

Girls are perking up after a week of really good flushing. Will start them back on nutes next watering and go with a feed / water / supplement / water rotation from here on out. Did a sample of coco in distilled water and the pH was 6.1. So I guess it was a salt buildup from not flushing good enough.