mixing GW phospate into solution? - The Planted Tank Forum
Old 12-10-2005, 09:22 PM Thread Starter
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mixing GW phospate into solution?

Just wondering if there are any brainiacs in here that can help me figure this out. I'm wanting to mix a 250ml or 500ml solution for phosphates. It is the K2HPO4 dry stuff found @ Greg Watson's. Just unsure of how much powder goes in the bottle. Right now I dose 1/32 tsp for my 20gallon every other day. Would be great if I could convert that into like 5 ml or something easy like that. Anyone done this before? Thanks
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Old 12-10-2005, 09:47 PM
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This calculator and this unit converter is what you need.

What I do is pick a bottle I want to use for the solution, and use the full capacity for "Amount of water to mix with" in the calculator. (By using the full bottle capacity, I don't have to measure water when making the mix.)

Then, I pick an easy measurement for dosing. Say I want to add 1ppm of phosphate to my tank with each teaspoon of solution. The unit converter tells me a teaspoon is 4.9ml. So, I'd be adding 1/4.9 = 0.2ppm/ml (rounded).

Then I play with the amount of solid fertilizer in the calculator until "Each ML of this solution that you add to your tank will add" reads close to 0.2ppm.

Working this through, 2.25tsp. of dry KH2PO4 in 500ml of water will produce a solution that raises your 20g phosphate by 1ppm (actually, 0.98ppm) per teaspoon. And converting 500ml to teaspoons, you have 101 1ppm doses of solution. Easy.

Tip: Label the bottle with the amount of water/solid fert, the dose size, ppm per dose, and size aquarium the dose is intended for. Avoids confusion and when it's time to refill, all the info you need mix more is right there.
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Old 12-10-2005, 10:33 PM Thread Starter
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Thanks for the reply. I wonder if this might work. For example, I want to dose 1/4 tsp using 5ml of solution for each dose. I have a 500ml water. Can i assume that = 100 doses @ 1/4tsp each? So 25 tsp to mix the solution. But then 25 tsp would make that 500ml into more like 625ml. since 1tsp = 5ml. so i would need to dose 6.25ml solution?

If that is correct, if 1/4 tsp = 0.25, then what does 1/32tsp =?
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Old 12-11-2005, 12:37 AM
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Quote:
Originally Posted by hir0
For example, I want to dose 1/4 tsp using 5ml of solution for each dose.
That's *awfully* strong. 5ml of solution is 1tsp, and you might have some difficulty getting 1/4tsp of solid to dissolve in 1tsp of water. Ignoring that, we continue...

Quote:
Originally Posted by hir0
I have a 500ml water. Can i assume that = 100 doses @ 1/4tsp each? So 25 tsp to mix the solution.
Yep.

Quote:
Originally Posted by hir0
But then 25 tsp would make that 500ml into more like 625ml. since 1tsp = 5ml. so i would need to dose 6.25ml solution?
A solid, when dissolved in a solvent, does not increase the volume of the solvent anywhere near as much as the original volume of the solid. The dissolved solid molecules kind of squeeze inbetween the molecules of the solvent, without forcing them apart. It's like taking a 3" layer of aquarium gravel and then pouring some sand on top and stirring - the sand will trickle down in between the voids and you still have a 3" layer.

For all practical purposes, you can assume you will still have 500ml of solution after adding the solute.

Quote:
Originally Posted by hir0
If that is correct, if 1/4 tsp = 0.25, then what does 1/32tsp =?
0.03125, obtained by dividing 1 by 32 on a calculator. So your hundred doses would be 3.125tsp, or 3 1/8 tsp. in common fractions.
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Old 12-11-2005, 10:46 AM Thread Starter
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Thanks Dark Cobra. That's about what I ended up doing. I put 1 tbsp and mixed in enough water to make 500ml. That's like 5.2 ml for my 1/32 tsp dose. Not bad, about 96 doses will last a while.
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Old 12-12-2005, 04:24 PM
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Ok, since you were struggling, I wanna make sure you know what you mixed up

So 1tbsp in 500 ml of water...that means each 1mL of solution is going to increase PO4 by .27ppm in your 20 gallon.
That's a pretty decent solution.

Don't think of it as "My dose is 5mL"...your dose is whatever you need. Today it might be nothing, next Wednesday you might need 7mL (1.5ppm of phosphate).
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