Getting the dose right is the single biggest thing you can do for plant health — and it’s simpler than most people expect. The problem isn’t usually the wrong product, it’s dosing inconsistently, guessing the amount, or following instructions designed for a completely different tank setup. This guide gives you a clear starting point and explains exactly how to adjust from there.

The standard dose: 1ml per 10 litres, once daily

For a medium or high light planted aquarium, the standard Aquafertz dose is 1ml of macro solution and 1ml of micro solution per 10 litres of tank water, added once daily. That’s the whole formula. Simple, repeatable, and easy to build into a routine.

So a 60-litre tank gets 6ml of each solution per day. A 100-litre tank gets 10ml of each. A 200-litre tank gets 20ml of each. The included dosing syringes make measuring accurate and quick at any tank size. The whole process takes under a minute once you’re in the habit.

Dose your macro solution first, then your micro solution. Add both just before your lights come on in the morning — this way plants begin absorbing nutrients immediately as photosynthesis starts, which keeps free nutrient levels in the water as low as possible at any given time.

Daily dose by tank size — quick reference

Medium / high light tanks. Halve for low-light or shrimp-only setups. Double for very high light with CO₂ injection.

Why light level determines your dose

Fertiliser dose is directly tied to how hard your plants are working — and that’s determined primarily by light intensity. More light drives faster photosynthesis, which means plants consume nutrients more quickly and need more supplied to keep pace.

If you dose for a high-light tank but only run low lighting, you’ll end up with excess nutrients in the water that plants can’t consume fast enough — which feeds algae. The relationship between light, nutrients, and plant health is fundamental. For more on the algae connection, see our guide: why algae appears even in well-lit tanks.

Consistency matters more than precision

The single most important thing about aquarium fertiliser dosing isn’t getting the amount exactly right — it’s doing it every single day without gaps. Plants cannot store nutrients for more than a day or two. Miss three days and growth stalls noticeably. Miss a week and you’ll see yellowing beginning, and potentially an algae response as the plants weaken and stop competing effectively.

The simplest approach: keep both solution bottles right next to your tank. Every morning, before the lights come on, squirt the right amount of each into the water. The process takes 20 seconds once you’re in the habit — less time than feeding fish.

How to adjust when something’s not right

The advantage of using individual compounds is that you can adjust just the element that’s causing the issue rather than changing your whole formula. Here’s what the signs tell you:

Yellowing between leaf veins on older leaves — increase MgSO₄. New leaves coming in pale or white — add more Iron DTPA. General yellowing and slow growth — increase KNO₃. Holes or yellowing at leaf margins — increase K₂SO₄.

For the complete guide to reading what your plants are telling you, see: Why Are My Aquarium Plant Leaves Turning Yellow?

Adjusting for a high fish load

If your tank has a significant fish population, fish waste is already adding nitrogen (nitrate) and phosphorus to the water. In a heavily stocked tank, you may find that reducing your KNO₃ dose and potentially your KH₂PO₄ dose makes sense — while keeping potassium, magnesium, and iron at standard levels.

The best way to dial this in is to test nitrate periodically. If your nitrate is already at 10–20ppm from fish waste alone, you have less need for additional nitrogen from KNO₃. This kind of precision adjustment is exactly what individual compounds allow — something no pre-mixed liquid fertiliser can offer. For more on the liquid vs powder comparison, see our guide: Aquarium Plant Fertiliser: Liquid vs Powder.

When to do water changes

Unlike the Estimative Index dosing method which requires large, scheduled weekly water changes to reset the tank, daily micro-dosing uses a TDS-based approach. Rather than changing water on a fixed schedule, you monitor TDS (total dissolved solids) with a cheap TDS meter and perform a 50% water change when your tank TDS exceeds your tap water TDS by more than 100 µS/cm.

For example: if your tap water reads 300 µS/cm, change 50% when the tank reaches 400 µS/cm. This prevents nutrient and mineral build-up while keeping maintenance to a minimum. You change water when the numbers tell you to — not before and not according to an arbitrary weekly schedule.

A basic TDS pen costs a few pounds and is genuinely one of the most useful bits of kit you can add to a planted tank setup. It removes all guesswork from water change decisions and helps you understand how quickly your tank accumulates dissolved solids at your current dose level.

How long does the kit last?

At the standard dose for a 100-litre tank (10ml macro + 10ml micro per day), the Aquafertz Full Kit gives you approximately 6–8 months of daily dosing from each 500ml solution bottle. For smaller tanks the kit lasts considerably longer — a 30-litre nano dosed at 3ml per day will get well over a year from one kit.

Because each compound is available to purchase individually, you only ever reorder what runs low. Typically KNO₃ goes first as it’s used in the highest quantity in the macro bottle. There’s no need to buy a complete new kit every time — just top up the individual compound and carry on.

This approach is significantly more economical than pre-mixed liquid fertilisers which force you to buy a whole new bottle regardless of which element you’ve actually run through. Over a year, the saving is substantial — see the full cost comparison in our guide: Aquarium Plant Fertiliser: Liquid vs Powder.

Everything you need to get started