Aptus - Substrate Buffer Liquid

A liquid pH buffer for your substrate: micronised calcium in liquid form, given as a separate watering whenever the pH of your medium is too low. At any point in the grow and on any substrate, diluted at 20 ml per 10 litres of water.

A watering that is not a feed

The most important thing about this bottle is in two short sentences from Aptus: do not mix it with other products, and do not adjust the pH of the water. So you make up a separate tank with nothing but water and buffer, and give one watering with it. No base feed, no boosters, no pH down.

That feels odd if you are used to everything going into one tank, but it follows from what the product does. It is meant to raise the pH of your substrate. If you first brought the water down with an acid, you would be working in exactly the opposite direction. Aptus describe the application as a flush of the medium: you run the buffer through the substrate, and that puts it where it needs to be. The watering after that is simply your normal feed again.

Measure first, then measure again

Aptus tie this bottle firmly to measuring. Their advice is to test the substrate before use, so you know where the pH of your medium actually is, and they describe a method for that test on their website. Between applications you measure the runoff again, to check you are staying within the range you want.

That is the only order that makes sense anyway. Something that raises pH is given when the pH is too low, not because it appears on a schedule. The pH of your irrigation water tells you little here, since you set that yourself. What matters is what happens in the root zone, and you read that from the substrate or from the water draining out of it.

If you would rather not measure, Aptus give a rule of thumb: once, a month after planting. That is an average moment, not a measurement. It works as a safety net for anyone not following it closely, but on any given day a grower who measures knows more than the rule does.

Where the liquid fits next to the powder

Aptus also make this buffer as a powder, Substrate Buffer Powder, and treat the two as a pair. The powder is mixed through the substrate once, before you plant. Halfway through the grow that is no longer possible without disturbing the roots, and that is where the liquid comes in: you give it by watering can or through your irrigation, when a measurement calls for it.

It also means this bottle works on substrates you cannot mix a powder into. You cannot turn over a rockwool slab or block, but you can flush it. Aptus describe it as suitable for all substrates.

Dosing and measuring out

The dilution is 20 ml per 10 litres of water, or 1 in 500. That is a good deal stronger than most additives, which suits a product you give as a correction rather than every week. A 250 ml bottle makes 125 litres of irrigation water, a litre makes 500 litres.

The calcium is held in the liquid as micronised particles. So shake the bottle well before measuring, to make sure you get the intended dose. Aptus state that the product is free from chlorides, ballast salts and contaminants, and that it also supplies calcium to the plant.

Available sizes

Technical Specifications:

• Type: liquid pH buffer for substrates
• Manufacturer: Aptus
• Contains: micronised calcium in liquid form
• Dose: 20 ml per 10 litres of water (1 in 500)
• When: when your substrate pH is too low, at any point in the grow
• Without measuring: once, a month after planting
• Mixing: not with other products, and do not adjust the pH of the water
• Application: as a flush through the substrate
• Substrate: all substrates
• Free from: chlorides, ballast salts and contaminants

Frequently asked questions

Can it go in my nutrient tank?
No. Aptus say: do not mix with other products and do not adjust the pH. You give it as a separate watering with plain water.

How do I know whether I need it?
By measuring the pH of your substrate or your runoff. If it is too low, this is the correction. The pH of your irrigation water says little about it.

How often do I give it?
As often as a measurement calls for it. Measure again between applications. If you do not measure, Aptus suggest once, a month after planting.

What is the difference from Substrate Buffer Powder?
The powder is mixed through the substrate once, before planting. The liquid is given during the grow, if the pH drops along the way.

Does it work on rockwool?
Aptus describe it as suitable for all substrates. Because you flush it through rather than mix it in, it is the form you can actually use on rockwool.