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Planted aquarium fertilization regime

Maintaining an aquarium can mean the accumulation of a lot of little chores. Generally speaking, if it’s inconvenient then it won’t get done, so I try to automate as many tasks as I can. With a short list of inexpensive parts, DIY automatic fertilization is straightforward.

I fertilize my 75 gallon aquarium with carbon via CO2, macronutrients via various dry compounds, and micronutrients via a commercial preparation called Plantex. The carbon is dosed from a pressurized gas cylinder at a constant rate to achieve about 30 ppm, and most other nutrients are dosed as a liquid once a day. Phosphate and calcium will form insoluble precipitates with other ions in my liquid mix, so they’re dosed once a week via dry compounds when I do my weekly water change.

To automate the daily dosing, I mix up two weeks worth of fertilizer solution in a tall, skinny plastic container made to store loaves of bread (total unitasker product). A small powerhead runs for two minutes every day, pumping 1/14th of the solution into my aquarium. The solution is made up of:

  • about 4850mL of tap water
  • 9.5 g Plantex CSM+B
  • 24.0 g KNO3
  • 24.0 g K2SO4
  • 48.0 g MgSO4
  • 8mL HCl, added last

The result is that when the lights come on in the morning, there is at least 0.15ppm Fe, 3.7ppm NO3, 5.0ppm K, and 1.2ppm Mg in the water column. The constant CO2 supply and weekly addition of 1.25ppm PO4 via KH2PO4 and 12.75ppm Ca via CaCl2 complete my fertilization regime. It costs me about 25 minutes every other weekend in maintenance time.

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