Aluminum Sulphate


Okay, I have three seedlings 10 days old. They are all starting to get a little bit of yellow patches on the leaves, as well as stems look to be getting a bit red. I have them in Africal Violet Soil and have been watering with 8ph city rap water. After doing a lot of reading I decided these issues may be due to ph fluctuation. I have bought aluminum sulfate and added it to water to make the ph about 5.7 and watered them using this. I’m now having second thoughts… was this a very bad idea for my seedlings?


It is hard to say how bad this would be for your seedling, do you know what the ph in the soil was? But I don’t think it is a good idea to use this on seedlings.

The red stems and patches on the leaves might be from a PH imbalance causing nutrient lock out or toxicity. I am a little worried about the aluminum in the product you used.

But a more likely situation is as it is one of the easiest and most common mistakes new growers make with cannabis, or even almost any plant, that is a big cause of nutrient imbalance is over watering. The roots can not dry out bone dry, but cannabis roots love very airy soil that drains very well and the roots drown easily in too much water. Purple or red stems and leaf splotches are often a sign of over-watering.


Before the problems started, we transplanted from Rockwell cubes, took off the mesh. The soil PH was only tested before I put in the sulphate and it was at 7.7. When we transplanted, we did not water, only misted. Two days after transplanting, I watered just until I saw it come out the bottom (this water was 8ph). Leaves are also curling up along the edges which I forgot to mention in the first post and these symptoms were appearing the day before the major watering took place. The aluminum sulfate was bought from the garden section at home hardware and is specifically for plants. Hoping that makes it less bad. I have now bought ph down for my water and will not water again until the top layer of soil is completely dry. Hopefully they can bounce back from the overwatering. Thanks for all your help!!


I’m not worried about the aluminum as in being toxic to humans, nor necessarily the plant, I’m just not a fan of using aluminum and it can become toxic to plants in certain conditions. If you are going to transfer rock wool to soil, the rockwool block shouldn’t be a very big one at all, also the soil should be heavily amended to drain really well. Rockwool, being melted rock, and rocks are made of the minerals that tend to be more alkali in nature, i.e. silicon and calcium will often bring the PH up. I would have used magnesium sulfate instead, as the red could be signs of sulfur and/or, magnesium deficiencies, it could also be a calcium deficiency, but with hard tap water with a PH of 8, there is probably plenty of calcium available and all of these point to water logging of the roots which can happen when putting rockwool in soil, you really need the soil well amended.

I would have adjusted PH with a liquid acidify-er made for hydroponics as you have them in the rockwool or used lemon juice. Fresh squeezed lemon juice works very well in a pinch to bring high PH water down. Normally a ph of 7.7, all other things being equal, wouldn’t be a huge deal in a good soil, and would kinda self adjust in time with properly PH’ed watering and would even turn a little acidic on its own during flowering.

PH down is very good and I think is much better, as phosphorous is highly needed and used by the plant. If you are going to use a sulfate instead of magnesium sulfate, I prefer zinc sulfate, zinc being more highly needed and used than aluminum is needed by the plant as well, but you need to be sure of the concentrations as any of these can be toxic in too strong of amounts.


I would not add aluminum to my plants as a PH down. Go to the Auto parts store and buy some diluted sulfuric acid. (commonly known as battery acid refill) very inexpensive, and despite naysayers; This product is nothing more than diluted Sulfuric acid.

Coca Cola contains Phosphoric acid. This the common acid used in commercial PH down. I have been using the “battery acid” for years. I grow commercial crops in hydroponic greenhouses, and this is what I use for my MMJ. Hope this helps.

Best acid for use in hydroponics as a PH down. Boric acid (Extremely expensive). I use solubor (boron) as a micro nutrient and sulphuric acid as a PH down.

2nd best: Phosphoric acid. Also; Expensive, but the only way to buy for hydroponics and, it be affordable is diluted. I use MKP to balance not using Phosphric acid.

Best value: Sulfuric acid.

Just for future re: Hope this hels


Yup, most colas have phosphoric acid in them, Dr. Pepper does too. You can also buy food grade phosphoric acid pretty cheap, online or elsewhere. And of course as I said, PH down is phosphoric acid. Sulfuric acid is also good and likely even from an auto parts store is pretty much pure, and as long as it is pure sulfuric acid without any weird additives, and as Latewood has already said about this form of sulfuric acid, you should be good to go. These are all great alternatives to know about.