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DTW nutrient tank PH dropping

The-Fallen

New member
Hi I'm growing DTW in coco and I have a 60L nutrient tank, but I am having problems with the PH dropping to 4.5 after around a week.

I fill the tank with plain water with a pump in the bottom and leave it for 24+ hours.
I then mix up the nutes (currently using shogun) so the EC is where I want it and leave for a few hours until fully mixed.
I then set the PH to 5.8, the PH will stay around 5.8 for about a week and then when I go to feed the girls one evening it will read 4.5.

I have a high end EC and PH meter which is fully calibrated and has been checked against other meters.

My water comes out the tap at under 0.4 EC.

The nutrient tank has a mj1000 pump keeping everything mixed.

There is no wild temp swings where the tank is located, it sits around 18-19 degrees C.

Any help would be appreciated.

The-Fallen
 

f-e

Well-known member
Mentor
Veteran
Wild idea really, but is anything living in there? Evidence of slime on the tank walls perhaps?

My mind drifts to aquarium owners lowering pH with co2 injection. Could something be colonising your tank, then taking all the oxygen and leaving high co2 levels?

3 question marks. I'm really scratching. Why do you have a tank a week though. Huge tanks are rarely a good idea.
 

The-Fallen

New member
Wild idea really, but is anything living in there? Evidence of slime on the tank walls perhaps?

My mind drifts to aquarium owners lowering pH with co2 injection. Could something be colonising your tank, then taking all the oxygen and leaving high co2 levels?

3 question marks. I'm really scratching. Why do you have a tank a week though. Huge tanks are rarely a good idea.

That was my first though too, I should have mentioned that I bleached the tank out fully and started fresh.

The reason for the large tank is that I usually have a drip feed setup for multi feeds throughout lights on, but due to my current PH issues I'm not using it as I check the PH before I feed them in case it's miles out.
 

The-Fallen

New member
carbonic acid

Think I've found what I needed in "The Chemistry behind Coco Coir" by The.Cook


"H2O+CO2 -> H2CO3

Being H2CO3 an acid, water play its role as a base, actracting H+ from the newcomer and lowering pH till a 5.5 value.

Why till 5.5 and not more? I've said water act as base when toghether with someting MORE acidic. In that case, 5.5 is the equilibrium point. Maybe you are allready thinking that adding your pH+ would be a simple solution but think about it: if you raise the pH, water will be once again basic if compared to H2CO3, at that time will start to act as a base as before.

Seems frustating doesn't it? Well, actually it's a great thing: the fact is that water by its own has a very low inertia to pH adjustment. In other word, easily matches pH of surrounding substances."

The-Fallen
 

Tazard

New member
pH vs ppm guide

pH vs ppm guide

I hope some of you find this useful.
Taz
 

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