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Old 02-10-2019, 12:10 AM #1
Fourtay
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Root zone PH dropping - help!

Hello,
I grow in amended coco coir, 60% coco coir 40% hydroton.
I use the heads formula General Hydroponics 6/9 micro/bloom per gal water.

I currently water 3 times per day, automated system.
First irrigation is 20 min after lights on, second is 4 hours after lights on, 3rd is 8 hours after lights on

approximately 20% runoff

My starting tap water ranges from 0 PPM to 50 PPM on a Blue Lab meter.
I have seen this problem many times in the past and I do not know how to fix it.
This specific problem seems to happen after about day 30 of bloom.

This particular run I am at day 31 and I just took 3 seperate runoff readings and these were the results: Input pH / ppm = 6.0pH / 650 PPM / 1.3 EC
Cultivar A - 5.0 pH 650 ppm
Cultivar B - 5.3 pH 700 ppm
Cultivar C - 5.4 pH 680 ppm

What typically happens when I have this problem is the ph will continue to fall into the high 4 range, the plants will stop growing, the hairs will turn brown, natural oils / smells will die off and lose their odor.

some advice I have seen in the past has been:

Use calcium carbonate to buffer the water (I dont know how to do this?)

Use citric acid and then potassium hydroxide in concert and quicky feed to the plants to re-establish the lost buffer

Pre-buffer the starting water before adding nutrients via calmag or ph up to approximately 100-150 ppm


What I would like to know if anyone has seen this problem before or has corrected it and any suggestions.
Thank you in advance!
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Old 02-10-2019, 12:42 AM #2
TanzanianMagic
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Quote:
Originally Posted by Fourtay View Post
Hello,
I grow in amended coco coir, 60% coco coir 40% hydroton.
I use the heads formula General Hydroponics 6/9 micro/bloom per gal water.

I currently water 3 times per day, automated system.
First irrigation is 20 min after lights on, second is 4 hours after lights on, 3rd is 8 hours after lights on

approximately 20% runoff

My starting tap water ranges from 0 PPM to 50 PPM on a Blue Lab meter.
I have seen this problem many times in the past and I do not know how to fix it.
This specific problem seems to happen after about day 30 of bloom.

This particular run I am at day 31 and I just took 3 seperate runoff readings and these were the results: Input pH / ppm = 6.0pH / 650 PPM / 1.3 EC
Cultivar A - 5.0 pH 650 ppm
Cultivar B - 5.3 pH 700 ppm
Cultivar C - 5.4 pH 680 ppm

What typically happens when I have this problem is the ph will continue to fall into the high 4 range, the plants will stop growing, the hairs will turn brown, natural oils / smells will die off and lose their odor.

some advice I have seen in the past has been:

Use calcium carbonate to buffer the water (I dont know how to do this?)

Use citric acid and then potassium hydroxide in concert and quicky feed to the plants to re-establish the lost buffer

Pre-buffer the starting water before adding nutrients via calmag or ph up to approximately 100-150 ppm


What I would like to know if anyone has seen this problem before or has corrected it and any suggestions.
Thank you in advance!
1. The tapwater is very soft, so it might be best to a) use soft water nutrients, which have extra calcium and magnesium added or b) add calcium, magnesium and trace elements to the water by adding a pinch of Maerl or other magnesium lime to a quart of tapwater for a day, and then mix the clear runoff with 3 parts tapwater.

Quote:
I grow in amended coco coir, 60% coco coir 40% hydroton.
2. Why?

If you grow in straight up coco coir you:

- don't have to water as often because it just holds water longer
- create a more constant and stable environment for the plant
- coco coir isn't aeroponics - the plants won't die if they don't get watered for a day
- coco coir and hydroton have different pH's - Coco Coir has about 6.0, and hydroton has 7.0, and you end up with a medium with 6.0 pH and lots of 7.0 spots in it
- coco coir has lots of aeration already and doesn't need any amendments, all it needs is to dry out at least a little between feedings
- you can and should use perlite and hydroton as a drainage layer, enough to cover the drainage holes of smaller and bigger pots, respectively. Hydroton should be treated by being put in water for at least a couple of days, so they can uptake more water and don't dry out the plant roots; perlite should also be put in a tub and sprayed with warm water until it floats, stand for 10 minutes and then scoop up whatever floats this takes out the perlite dust and any metal or rocks left, it also allows mixes with perlite to be used multiple times because the dust doesn't turn the medium into cement, so to speak.

Last edited by TanzanianMagic; 02-10-2019 at 02:06 AM..
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Old 02-10-2019, 01:13 AM #3
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If you bring your tap up to 150 or 200 ppms with cal-mag that should fix it. You have more free hydrogen than hydroxyl ions. The Cal-mag will buffer the hydrogen. You may have to use more Cal mag, if you have used a lot of acid.
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Old 02-10-2019, 03:35 AM #4
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Quote:
Originally Posted by Creeperpark View Post
If you bring your tap up to 150 or 200 ppms with cal-mag that should fix it. You have more free hydrogen than hydroxyl ions. The Cal-mag will buffer the hydrogen. You may have to use more Cal mag, if you have used a lot of acid.
Thank you for the advice! I will give this a shot.
How do you mean used alot of acid?
I have only used PH up in the mixture.

The 6/9 fertilizer formula usually comes out to about 5.8 ph and 650 ppm, lately i have added Gen hydro ph up bringing it to 6.3 ph
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Old 02-10-2019, 11:35 AM #5
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Couldn't You raise your pH with calcium-mag and eliminate the pH up? Couldn't cal-mag buffer your feed without all that pH UP? BTW this is a very helpful thread for me, Thank you for sharing.
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Old 02-10-2019, 08:47 PM #6
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The problem isn't pH. The problem is that soft water doesn't have a buffering capacity.

So if you add nutrients with any kind of P in it, it will drag down the pH.

This is what you do: add a pinch of magnesium lime, which has calcium and magnesium in it, let it stand for a day and mix with tapwater at a 1:3 ratio.

Here is why. Hardness of water is determined by the presence of calcium and magnesum atoms in the solution.

See Figure 1.
https://www.canna-uk.com/hard_water_and_soft_water

It is always best to direct the pH through the medium. Coco buffers to a pH of 6.0, while hydroton very persistently buffers to a pH of 7.0. Which is ok in an organic grow.

Also... mixing 40% hydroton into the medium means there is 40% less space for roots. Again, this isn't hydro, where you can just increase the nutrient solution and the plant doesn't need a lot of rootspace. In coco and soil, more roots (at the right time) mean more and bigger flowers.

Last edited by TanzanianMagic; 02-10-2019 at 08:58 PM..
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Old 02-10-2019, 09:53 PM #7
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Would it be possible to use calimagic at 5 ml per gal to the tap water first then add my nutrients?

I am unable to let my tank water sit for more than a few hours as the plants dry out too quickly
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Old 02-10-2019, 10:02 PM #8
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What color are the plants? What shade of green do they have? If your plants are a dark green at day 30, your problem is most likely root rot from too hot of nutrients. If you're running moderate hybrids to heavy feeding indicas, 650ppm is going to be between find and a bit low and I wouldn't expect root rot.

Low calcium can also contribute to weak roots, easier rotting and pH dropping.
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Old 02-10-2019, 10:16 PM #9
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Firstly, measuring run off pH isn't an accurate way of monitoring root zone/substrate pH.

Secondly, you should be running coir specific nutrients (a nutrient developed specifically for coir growing) because in coir you need higher levels of Ca and Mg to counter CEC site binding of Ca and Mg.

With your water being so soft and the fact you are running non coir specific nutrients (terrible idea btw) you definitely need to be adding Cal Mag.


To pH buffer soft water predissolve 0.5 gram of citric acid per 10 litres (5 grams to 100 litres) and add to solution. This will drop pH a lot. Then correct the pH to desirable range by adding potassium carbonate. The carbonates and citrates act as an acid and its conjugate base creating a mild pH buffering system.
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Old 02-10-2019, 11:59 PM #10
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Quote:
Originally Posted by Fourtay View Post
Would it be possible to use calimagic at 5 ml per gal to the tap water first then add my nutrients?

I am unable to let my tank water sit for more than a few hours as the plants dry out too quickly
You should repot into straight coco with a perlite or hydroton drainage layer.

Mixing coir with 40% hydroton means 40% of the medium is not available for root growth, and hydroton doesn't hold any moisture at all.

Also, what is the Relative Humidity? If it's under 50% you might want to raise that.
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