TriPart Micro freshwater fertiliser

Reverse osmosis water or rainwater is not neutral water, it is empty water, and that distinction changes everything about how you manage the reservoir. Empty of calcium and magnesium, which this version of Micro compensates for by supplying two to three times more calcium nitrate than the hard-water version. Empty of bicarbonates too, and this is the point nobody anticipates: bicarbonates act as a buffer and hold the pH steady. Without them, pH drops the moment the concentrates are added, then shifts at the slightest event, a plant absorbing nutrients, a rise in temperature, a top-up of water.

Three habits are all you need. Measure the conductivity of your source water: with reverse osmosis it is close to zero, which is actually convenient, since everything the meter reads afterwards comes solely from the fertiliser and nothing else. Adjust pH last, after adding all three parts, and usually upwards: with this type of water it is the pH+ adjuster you will need, not pH-, and in fractions of a millilitre. Finally, check pH every two days rather than once a week until you know how your setup drifts. If your water comes from the mains instead and exceeds 70 mg of calcium per litre, you need the Hard Water Micro, and our article on pH regulation sets out the measurement method in full.

The one rule that matters at dosing can be summed up in a single sentence: each part is added to the water separately, never one into the other, rinsing the measure between each. The calcium in this bottle and the phosphorus in the Bloom, if brought into contact in concentrated form, produce an insoluble calcium phosphate that sinks to the bottom and becomes unavailable to anything. Diluted, they coexist without issue. The Starter Kit brings all three parts together in 500 ml so you can try the system.

Calculated at the full-growth dose of 1.2 ml per litre: the bottle size divided by the dose, then the bottle price divided by the size and multiplied by 120 ml, the amount required for a 100-litre reservoir.

These are litres of prepared solution, not weeks of cultivation: a 50-litre tank topped up every fortnight uses around 100 litres per month, while a 200-litre system uses four times as much. The key point the table doesn't spell out on its own: of the three bottles, it's the Micro that runs out first. Grow takes a back seat during flowering and Bloom stays low during growth, whereas Micro is used at a high dose from seedling to harvest, between 1 and 2 ml per litre depending on the stage. Many growers buy all three in the same size and find themselves reordering the Micro alone twice as often as the others. The Starter Kit illustrates this clearly: its three 500 ml bottles don't run out at the same time.

One final point, often decisive: the iron in this Micro is chelated, and therefore protected from precipitation, but only within a limited pH range. Above pH 6.8, it gradually becomes unavailable and young leaves will pale even when the dose is correct. Our article on pH regulation explains how to keep it in check, and our guide to deficiencies helps distinguish an iron deficiency from excessively high pH.