Aquarium Fertiliser Dose Calculator Method Guide: Per-Litre Targets
Most planted tank failures trace not to too little light or CO2 but to fertilisation that is either guessed or copied from a foreign forum without recalibration. The aquarium fertiliser dose calculator question requires three inputs: tank working volume, target nutrient ppm by element, and dosing frequency. This guide from Gensou Aquascaping at 5 Everton Park lays out per-litre target ranges, gives the conversion maths from dry salt to ppm, and provides a worked Estimative Index dose for a 100 L tank. The aquarium fertiliser dose calculator is straightforward arithmetic once you know the targets — and the targets vary by methodology, not by guess.
Quick Answer Rule of Thumb
For Estimative Index high-tech: NO3 20-30 ppm, PO4 1-3 ppm, K 20-30 ppm, Mg 5-10 ppm, Ca 20-40 ppm, Fe 0.5 ppm, traces dosed daily. For PPS-Pro lean dosing: NO3 5-10 ppm, PO4 0.5-1 ppm, K 10-15 ppm, Fe 0.1-0.2 ppm. Low-tech tanks rely on fish waste plus 1 mL per 50 L weekly of liquid all-in-one.
The Conversion Method
Each dry salt yields a known ppm contribution per gram per litre. Potassium nitrate (KNO3) dosed at 1 g per 100 L produces approximately 6.1 ppm NO3 and 3.9 ppm K. Monopotassium phosphate (KH2PO4) dosed at 1 g per 100 L produces 7.0 ppm PO4 and 2.9 ppm K. Potassium sulphate (K2SO4) at 1 g per 100 L gives 4.5 ppm K. Magnesium sulphate (Epsom salt) at 1 g per 100 L gives 1.0 ppm Mg.
The EI Weekly Schedule
Estimative Index dosing splits the weekly target across three macro doses (Mon, Wed, Fri) and three micro doses (Tue, Thu, Sat) with a 50-70 per cent water change Sunday to reset. The protocol assumes plants will never run out by overdosing past saturation, then resetting weekly. It works only with strong CO2 (30 ppm dissolved) and high light (100+ PAR at substrate).
Worked Example: 100 L EI Weekly
Target weekly dose: 25 ppm NO3, 3 ppm PO4, 30 ppm K, 0.5 ppm Fe. Calculations: 25 ppm NO3 ÷ 6.1 ppm/g per 100 L = 4.1 g KNO3 weekly, split as 1.4 g three times. 3 ppm PO4 ÷ 7.0 = 0.43 g KH2PO4, split as 0.14 g three times. K shortfall after KNO3 (already 16 ppm) and KH2PO4 (already 1.2 ppm) = 12.8 ppm needed via K2SO4 = 2.85 g weekly. 0.5 ppm Fe via CSM+B at 0.13 g three times.
Worked Example: 60 L PPS-Pro Daily
PPS-Pro dosing aims at constant low-level nutrients without water change resets. Daily targets: 1 ppm NO3, 0.1 ppm PO4, 1 ppm K, 0.05 ppm Fe. For 60 L: 0.1 g KNO3 daily, 0.009 g KH2PO4 daily, balance K with K2SO4. Most hobbyists pre-mix concentrated stock solutions to dose mL rather than weighing milligrams. Bottle stocks from the ferts range avoid the scale precision issue entirely.
Worked Example: 200 L Low-Tech
Low-tech tanks without CO2 should not run EI — excess nutrients without matching CO2 trigger algae. Dose 5-10 ppm NO3 once per week post-water-change, plus weekly 0.5 ppm Fe. Total weekly: 1.6 g KNO3, 0.5 g CSM+B. Many hobbyists use a comprehensive liquid like Tropica Specialised at 6 mL weekly per 50 L for 200 L = 24 mL weekly — easier than dry salts at this dose level.
Singapore-Specific Variables
PUB tap brings in 2-4 dGH, meaning calcium and magnesium come pre-dosed at roughly 15-25 ppm Ca and 3-6 ppm Mg from the kitchen tap. EI calculations should subtract the tap baseline before adding GH boosters. Soft tap also limits potassium baseline — K supplementation matters more in Singapore than in hard-water cities. Use a test kit for NO3, PO4 and KH at minimum.
Common Pitfalls
Dosing EI levels into a low-light or low-CO2 tank produces algae, not growth. Forgetting that KNO3 and KH2PO4 both contribute K leads to K overdosing. Mixing macro and micro stock solutions in one bottle precipitates iron phosphate within hours. Calculating with gross tank volume instead of working volume overdoses by 10-15 per cent. Skipping the weekly water change in EI accumulates nutrients past 60 ppm NO3.
When to Override the Calculator
Visible plant deficiency overrides target ranges — interveinal yellowing on stems means iron, pinholes on Anubias means potassium, stunted new growth means nitrogen. Heavily stocked tanks generate ample N and P from waste, requiring K-only supplementation. Shrimp tanks need leaner dosing because copper traces accumulate. Adjust based on plant response over weeks, not the formula in isolation.
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