Rex's Planted Tank Guide

Your Source Of Information For Planted Aquariums, Lighting, CO2, Ferts & Substrate

Dosing Dry Fertilizers in the Planted Tank.

Ok, it seems to me that there is a lot of confusion out there about how to cheaply dose a planted tank with Dry Fertilizers. So here we go. First off you need a source of Dry Fertilizers. Check out www.bestaquariumregulator.com Next thing is to know what you need to buy.

  • KNO3 aka Potassium Nitrate is used to primarily dose nitrates or NO3. It does have the side effect of dosing a small amount of potassium.
  • KH2PO4 or Mono Potassium Phosphate is used for dosing phosphates or PO4.
  • K2SO4 or Potassium Sulfate is used for dosing potassium.
  • Plantex CSM+B is a trace mineral mix.
  • A gallon or so of RO/DI or distilled water.

Then you need to to go Chuck Gadd's site and download his Windows version of his calculator. If you are not running Windows then tough.

These are the big four. You can use Magnesium Sulfate to dose magnesium but if your General Hardness is over 4° and you do regular water changes then Magnesium should not be a problem. Yeah I know it's in the PMDD formula but that's because they had really soft water. You can use Calcium Carbonate to increase both kH and gH but I prefer to use baking soda for kH and Calcium Chloride for gH as they both dissolve a lot quicker.

Ok, on to the show. I am going to assume that you have the dry ferts and a supply of bottles that will hold around 300 ml of water. I will also assume that you are smart enough to have a set of measuring spoons and know the difference between a tablespoon and a teaspoon and that you know that when using measuring spoons you always use level measurements. If you don't know these things then just read this paragraph again and again till it sinks into your thick skull.

Mix Solutions

Ok, now we are going to mix solutions using 250 ml of water.

For the KNO3 you want to mix 16.8 grams or 3 teaspoons or one tablespoon (did you know there are three teaspoons in a tablespoon?) into 250 ml of water. Each ml of this solution will give you 1.08 ppm of NO3 in 10 gallons of water. Note: I did not say in a 10 gallon tank I said in 10 gallons of water. Don't know how much water your tank actually holds? Tough. You will also get the side benefit of dosing 0.68 ppm of Potassium in your 10 gallons of water at the same time.

Want a strong solution? Then mix 67.2 grams or 12 teaspoons or 4 tablespoons of KNO3 in 250 ml of water and this will give you a solution that will dose 4.34 ppm of NO3 in 10 gallons of water and 2.74 ppm of potassium for each ml dosed. You can also use Chuck's calculator to figure out how to dose KNO3 dry directly into your tank.

For dosing KH2PO4 you need to mix 7.2 grams or 1.5 teaspoons or 0.50 tablespoons into 250 ml of water. Each ml of this solution will 0.53 ppm of PO4 in 10 gallons of water.

For dosing K2SO4 don't bother to mix a solution. Dose it dry. 1.5 grams or ¼ teaspoon of K2SO4 will dose 10 gallons of water to 17.72 ppm. Take a bit of your tank water and pour the K2SO4 into it. Then mix till dissolved and pour back into the tank.

For Plantex CSM mix 1 tablespoon or three teaspoons into 250 ml of water and dose 4 ml of this solution 3 times a week into 10 gallons of water. You can go higher or lower than this dose based on the observation of your aquarium.

Amount Of Dosage *warning*

If you are dosing dry Ferts directly into your tank “pay close attention” to what you are doing and what I'm about to tell you.

  • ¼ teaspoon of KNO3 will raise 20 gallons of water to 11.25 ppm of nitrates. If your test kit doesn't reflect this change then either RTFM of the test kit several times till it sinks into your thick skull or get a new test kit. NEVER test your test kit in your tank.
  • ¼ teaspoon of K2SO4 will raise the potassium levels in 20 gallons of water to 8.25 ppm.
  • ¼ teaspoon of KH2PO4 will raise the PO4 levels in 20 gallons of water to 12.86 ppm.
  • Plantex CSM+B will dose traces and iron

And here is the info another way.

  • 0.3 grams of KNO3 will raise the nitrate level of 10 gallons of water 4.84 ppm
  • 0.1 gram of KH2PO4 will raise the phosphate level of 10 gallons of water 1.84 ppm
  • 1.0 gram of K2SO4 will raise the potassium level of 10 gallons of water 11.82 ppm

So now if you can do basic math you can figure out the dose for your tank. I doubt this will put an end on the forums to the constant “how much do I dose for XX size tank”. But I can always hope.

ALWAYS BE SURE YOU KNOW WHAT YOU ARE DOSING.

MIXING UP KH2PO4 AND PLANTEX CSM+B OR IRON CAN CAUSE PROBLEMS.

ALWAYS KNOW WHICH SIZE MEASURING SPOON YOU ARE HOLDING.

INSTEAD OF USING MEASURING SPOONS GO TO eBay AND SEARCH FOR “DIGITAL GRAM SCALES” A SCALE THAT IS ACCURATE TO 0.1 GRAMS WILL RUN YOU UNDER $20 AND WORKS GREAT.

ALWAYS KEEP IN MIND THAT THERE IS NO SUCH THING AS WEAK KNO3 FROM ANY OF THE COMMERCIAL SOURCES.

ALWAYS KEEP IN MIND THAT THERE ARE SOME PEOPLE WHO ARE NOT MENTALLY CAPABLE OF DOSING DRY FERTS DIRECTLY INTO THEIR TANK AND YOU MAY BE ONE OF THEM.