Aptus - Substrate Buffer Powder

A powdered pH buffer that you mix through your substrate once, before you plant. Micronised calcium that raises the pH of your medium and then keeps it steady. The dose is 50 grams per 50 litres of soil, and double that on coco.

You dose per litre of substrate, not per litre of water

This is one of the few products in the nutrients section that never goes into a tank. The dose is given not per litre of water but per litre of substrate: 50 grams per 50 litres of soil, or 1 gram per litre, and 100 grams per 50 litres of coco, or 2 grams per litre. You mix the powder thoroughly through the substrate before planting, and that is the job done.

Because the dose is tied to your substrate, you work out your quantity from your pots rather than your watering can. A 20 litre pot of soil gets 20 grams, the same pot of coco 40 grams. Ten 11 litre pots of coco need 220 grams between them. A 1 kilo bag therefore covers 1000 litres of soil or 500 litres of coco, and the 10 kilo bag ten times that.

Mixing is easiest in a tub or on a sheet, with the substrate loose, before it goes into the pot. The powder needs to be spread evenly: a spot where it sits in a clump gets too much, and the rest of the pot too little.

Giving coco a second run

Aptus mention one use you might not expect: upgrading used coco so it can be grown in again. If you keep your coco after a grow, the next round starts in a substrate that already has a full crop behind it. The powder is the way to give that substrate a fresh buffer before the new plants go in.

It fits exactly with how the product works. The powder does its job at the start of a grow, while the substrate is still loose and can be mixed through. With reused coco you have that moment anyway: between two grows, with the coco out of the pot. Use the coco dose for this, 2 grams per litre.

Once, and after that the liquid

Once a powder is in the substrate, you cannot add more halfway through the grow without disturbing the roots. For that, Aptus make a liquid version, Substrate Buffer Liquid, which you give as a separate watering if the pH drops along the way. Aptus treat the two as a pair: the powder lays down the buffer at the start, the liquid tops it up when a measurement calls for it.

What it does, and when it does not

The calcium in the powder acts as a pH buffer in the substrate: it raises the pH of your medium and then keeps it stable. That makes it a product for substrate that is too acidic or tends to become so. It is not something to push an already correct substrate higher, and it does not replace feeding. It also supplies calcium to the plant, and Aptus state that it is a natural product, free from chlorides, ballast salts and contaminants.

Aptus only give doses for soil and coco. Rockwool slabs and blocks cannot be mixed through in any case. There, the liquid version is the form that fits.

Available sizes

Technical Specifications:

• Type: powdered pH buffer for substrates
• Manufacturer: Aptus
• Contains: micronised calcium in powder form
• Dose for soil: 50 grams per 50 litres (1 gram per litre of substrate)
• Dose for coco: 100 grams per 50 litres (2 grams per litre of substrate)
• Application: once, mixed thoroughly through before planting
• Also for: upgrading used coco for reuse
• Free from: chlorides, ballast salts and contaminants

Frequently asked questions

Can I dissolve it in water and pour it on?
No, it is mixed through the substrate. If you want to give a buffer by watering can during the grow, Substrate Buffer Liquid is made for that.

How much do I need for my pots?
1 gram per litre of soil and 2 grams per litre of coco. A 15 litre pot of soil therefore gets 15 grams, and of coco 30 grams.

Why does coco get double?
Aptus give that dose but do not explain why. We stick to their figure and do not fill in a reason of our own.

Can I add it during the grow?
Aptus prescribe it once, before planting. If the pH drops along the way, use the liquid version.

Does it work on rockwool?
Rockwool cannot be mixed through, and Aptus only give doses for soil and coco. Use the liquid version there.