Help -I can’t get the pH down of my soilless growing medium PH down

[Franimal]

New grower here. Partner and I have around 25 teenage plants indoors under MARS ts1000 lights.
Growing medium: mix of coco (1/3) and ProMix (2/3)

issue is that the growing medium pH is stuck around 7 which Im pretty sure is causing issues with nutrient uptake. Some of the smaller ones have red stems and dehydrated looking leaves.

I had some luck watering with 5 pH water previously and saw another post on doing an acid drench of 4-4.5 water, but my partner wants to keep using 6 pH.

What should I do? How can I get this growing medium more acidic and have the ph stay there? It always seems to return to 7 within a day.

Using Rootfarm pH down.

 

[jguit]

what are you feeding your plants and at what rate? watering practices? temps/rh? light distance?

Are you using just that one light?

 

[Franimal]

what are you feeding your plants and at what rate? watering practices? temps/rh? light distance?

Are you using just that one light?

Watering with these a couple times a week. 5 ml of each per litre as per the instructions and supplementing with a bit of fish and a B vitamin boost. Watering until some but not tons of run-off, usually every two days. I’ve noticed this growing medium dries a lot faster than soil.

Yes just the one light on them for now. We have two more of these lights on other stuff but may be able to pivot one over to these in a month. Not sure if the height but you should be able to see from the one picture.

temperature has been in a good range of 68-75 g and humidity around 55-65

 

[Maxwax]

I think theres heat and light stress on the new growth and that light looks a little close? Could there be a Magnesium deficiency because of the Coco Coir?

 

[Moshmen]

My 2sense is it’s your mix of coco and promix - in my opinion u are going to continue to have problems. My suggestion is fairly extreme comparatively but I would transplant asap! Pick one medium promix or coco they are different growing methods and require different habits

 

[Billymgb]

I use coco coir and pro mix HP mixed at 50 50 and had no problems. I think your problem is your watering like its soil. you can feed these 2-3 times a day. Also you do need a cal mag mixed with your nutes on every feeding. As far as feeding (watering) with coco you should have some run off every time. There is a good read on here on how to grow in coco. Good luck my friend.

 

[Franimal]

I use coco coir and pro mix HP mixed at 50 50 and had no problems. I think your problem is your watering like its soil. you can feed these 2-3 times a day. Also you do need a cal mag mixed with your nutes on every feeding. As far as feeding (watering) with coco you should have some run off every time. There is a good read on here on how to grow in coco. Good luck my friend.

It’s so true, and I didn’t realize how different it is growing in soilless mediums. Are you saying I don’t need to worry about over watering? How often would you give nutrients?
I have Cal Mag coming soon so will start to supplement with that but should I worry it will add to the alkalinity? Do you have any suggestions to bring the pH down? If I don’t have to worry about overwatering then I could water the bad plants more often with low pH water. I’d love to check out that article you mentioned. Can you post a link?

 

[Franimal]

My 2sense is it’s your mix of coco and promix - in my opinion u are going to continue to have problems. My suggestion is fairly extreme comparatively but I would transplant asap! Pick one medium promix or coco they are different growing methods and require different habits

Interesting thanks! Maybe I’ll try that with a couple. Any suggestions on lowering pH?

 

[jguit]

I would consider either using promix HP or coco.

ProMix is a bit more soil-like IMHO as far as watering practices.

 

[Moshmen]

Interesting thanks! Maybe I’ll try that with a couple. Any suggestions on lowering pH?

It’s prolly the coco you added ? Did you treat or wash it?
As far as ole boy up there running 50/50 it’s only his 1st or 2nd grow I bet it is not as smooth as he says buts that’s my experience and opinion .

promix is very easy and forgiving in my opinion

 

[Peat_Phreak]

The bicarbonate level in your presumed tap water can be the source of the problem here. If your bicarbonate is too high, you can properly pH your water from 5.5-6.0 and still run into rising pH issues over time. What is the PPM of your presumed tap water.

 

[Peat_Phreak]

And I agree that choosing coco OR peat is the best option either right now or definitely for next time. Peat is easier. Do coco if you want to high frequency feed multiple times a day. I feed peat 15x a month.

 

[GanjaFarmer24]

Whats your temp and humidity look like?
I wouldn't worry about adjusting ph in the soil too much; the rhizosphere around the roots keeps itself in a good range.
Coco can suck up all your magnesium if its fresh; sprinkle a teaspoon of unscented epsom salt and a tablespoon of worm castings around the base of the plants every 2 weeks.
Edit: also don't put your pots directly on the floor, cold roots are bad.

 

[Franimal]

The bicarbonate level in your presumed tap water can be the source of the problem here. If your bicarbonate is too high, you can properly pH your water from 5.5-6.0 and still run into rising pH issues over time. What is the PPM of your presumed tap water.

How do you test PPM?

 

[Franimal]

It’s prolly the coco you added ? Did you treat or wash it?
As far as ole boy up there running 50/50 it’s only his 1st or 2nd grow I bet it is not as smooth as he says buts that’s my experience and opinion .

promix is very easy and forgiving in my opinion

It was pre washed Canna Coco

 

[jguit]

How do you test PPM?

I'd first check for a water report from your municipality. If you can't get one you'd have to have a tap water analysis done. I totally recommend it. It's not very expensive.

 

[Franimal]

I'd first check for a water report from your municipality. If you can't get one you'd have to have a tap water analysis done. I totally recommend it. It's not very expensive.

Once I have that, is there a chart or anything explaining healthy ranges?

 

[jguit]

Once I have that, is there a chart or anything explaining healthy ranges?

I'm not sure if there's a chart but If you post the results, I'm sure folks will point you in the right direction.

 

[mysticepipedon]

Before doing anything drastic, consider that your plants aren't actually showing any deficiency symptoms. You are trying to keep your plants happy, not your pH pen.

Your stems are green. Red petioles (leaf stems) are nothing to worry about. It seems like LEDs turn petioles red.

I think I would stick with feeding them with your pH 6 solution.

 

[Peat_Phreak]

How do you test PPM?

buy a ppm/EC meter for $25. It's also useful for checking solution strength. If your tap water is higher than 200ppm, it can cause rising pH problems. However a ppm/EC meter doesn't tell you the bicarbonate level. That is the most important number to know. Bicarbonate can be estimated by your total ppm. A water report can also determine the bicarbonate level.