Dosing extra potassium question - The Planted Tank Forum
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post #1 of 3 (permalink) Old 08-30-2014, 01:02 AM Thread Starter
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Dosing extra potassium question

For dosing extra potassium, does it make sense to prepare a homemade dry fert solution with K2SO4? Currently I'm using Seachem Potassium but that is not going very far... I'm trying to dose so that my levels are around 25-30 ppm at least, as I have quite a bunch of potassium sucking plants and potassium deficiency is the one symptom I am seeing regularly (even my poor wendtii got a hole today).

I plugged in what I wanted into

and got this

To reach your target of 30.0 ppm K you will need to add 759.215 g K2SO4 to your 500.0 mL dosing container. Add 5.0 mL of that mix to your 30.0 US gal aquarium to yield
Element ppm/degree
K 30.00
S 12.30

The solubility of K2SO4 at room temperature is 120 mg/mL. You should adjust your dose.

I'm not sure what the part in red means, but I'm guessing that it means not all of the dry fert would get mixed into the water if I add that many grams to the 500ml?
I'm not very good at either chemistry or math, if anyone can help clarify this and possibly help me figure out a potassium solution mixture that would work, I'd be much obliged.
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post #2 of 3 (permalink) Old 08-30-2014, 02:41 AM
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Yes, it will not dissolve in that little water. It's better to dose dry and save yourself the trouble.
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post #3 of 3 (permalink) Old 08-30-2014, 02:41 AM
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Dose it dry for all but the smallest tanks. (30 gallon tank is not a problem at all to dose dry)

Here is what I would do:
Read the Estimative Index chart for my tank size. I see you have used 30 gallons in your example, so look at the EI for 20-40 gallon tanks.

Instead of KNO3, use the same amount of K2SO4.
Dose it the same way as is suggested. That would be 1/4 tsp (dry) 3 times per week.

Yes, the part in red suggests that you use a larger container to make the mix, if you want to make it into a liquid. Try telling it you will be using a 1 liter container. You would then dose twice as much because you are making a more diluted solution.

Lets go back to the EI dose, and try to make a liquid.
If you put 1/4 tsp K2SO4 in ANY size container of water, you would add all of it in one day. So lets just say you put it in 1/4 cup of water, swirl it around for a few seconds, then dump it into the tank. Every day. You get tired of doing that rig-marole and decide to make a weeks worth all at one time.
Put 3/4 tsp in 3/4 cup of water and spread that out over 1 week (3 doses of 1/4 cup each). That is working well, but you think you can do better.

Put 6/4 tsp in 3/4 cup of water and you would spread that out over 2 weeks, but note I did not increase the water? Now you would add just 1/8 cup each time you dose. But because you have put 6 x 1/4 tsp in there, you have 6 doses.

You can go on and figure out however much you want to make up at a time.

OK, lets say you want to use the container holding 500 ml.
You might dose 10ml at a time into your 30 gallon tank. So the 500ml container holds 50 doses.
At 1/4 tsp per dose, you would add
50 x 1/4 tsp to the container. (mumble... mumble...) this comes out to so close to 4 tablespoons that I would do it that way. (12.5 tsp to be exact)
I KNOW that much will dissolve, because that is the way I do it.
50 doses, dosed at every other day (that is, 3 times per week) will give you over 4 months worth of fertilizer.
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