This guide is for CO2 injected tanks only.

When I started planted aquariums, I dived straight into Seachem range of fertilisers. I did my studies and research online and it seems like a clear choice.

However, the BIGGEST problem I faced in my research was that there is no dosing formula to adhere to. Well, some argued that it depends on how much plants you have and what kind of plants you have, what kind of lightings, etc.

There were also heaps of different types of calculators online that will do everything except giving the answer that you are looking for.

Well, I have devised my very own formula through the years. You can try my formula and make adjustment accordingly.

At least it is a starting point for a lot of people.

What Ferts Do you Need?

Flourish Nitrogen

Flourish Phosphorus

Flourish Potassium

Flourish Iron

Flourish (Comprehensive)

Base Dosage Amount

The base dosage amount is based on 10 gallon. If you are dosing for a 55 gallon, simply multiply the dosage by a factor of 5.5. If you are dosing for 75 gallon, then multiply the amount by a factor of 7.5.

If you are dosing for a tank smaller than 10 gallon, for example a 6 gallon tank, simply multiply by a factor of 0.6.

Flourish Nitrogen0.51ml
Flourish Phosphorus1ml
Flourish Potassium1.28ml
Flourish Iron0.8ml
Flourish (Comprehensive)0.61ml
The base dosage WILL ONLY WORK with my dosing regime. DO NOT use it as a daily dose.

Dosage Regime

I do not dose ferts on water change day. I have no scientific findings on this. This is based on my own personal trials.

SaturdayWater change dayNo dosing
SundayNitrogen0.51ml
Phosphorus1ml
Potassium1.28ml
MondayIron0.8ml
Flourish (Compre)0.61ml
TuesdayPotassium1.28ml
Iron0.8ml
WednesdayNitrogen0.51ml
Phosphorus1ml
ThursdayIron0.8ml
Flourish (Compre)0.61ml
FridayPotassium1.28ml

New Tank Dosing

If you are dosing for a new tank, I would suggest reducing the dose amount by half. In addition, reduce your photo period to just 5-6 hours per day.

You can check for algae growth daily. If you can see algae growing within a couple of days then dim your lights if your light has that function. If your lights do not have dimming function then try raising it higher.

Dosing Apparatus

Seachem recommends using the cap screw threads as a guide. Well I started off using that but it sucks.

For a while I was using a surgical syringe to do that. But using a surgical syringe can create danger if you have small children. Using a surgical syringe without the needle is messy. You will need to first pour out the ferts into the cap or a container before you can draw the amount.

And the other problem is surgical syringe is not very accurate.

What I am using now is a single channel lab pipettor. You can get a one cheap for about USD15-25. You will thank me later for this suggestion.

The pipette is adjustable to 0.01ml for some, but of course we do not need that kind of accuracy for ferts dosing. Furthermore, it can reach directly into the ferts bottle to draw the ferts. Easily one of my best purchases!

Where to buy the Pipettor

You can get it cheap from AliExpress. USD23 with shipping.

I got mine (in the photo above) from Tao Bao for a mere USD14. Tao Bao link here. You can check out how to purchase and ship to your country from Tao Bao here.

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