KNO3 doesn't dissolve well!!! - The Planted Tank Forum
 
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post #1 of 14 (permalink) Old 09-11-2004, 02:50 AM Thread Starter
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KNO3 doesn't dissolve well!!!

My 6 tablespoons potassium nitrate doesn't dissolve well the the 250ml of water I add to it, how do i get it from not crystalizing on the bottom?

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post #2 of 14 (permalink) Old 09-11-2004, 03:17 AM
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Are you using tap or RO/Distilled? The tap can already contain K+ or NO3- ions, which will lower the solubility of KNO3 (Common ion effect). Try using RO/Distilled and/or use 500mL of water - dose twice as much.

You can't go wrong with RO/Distilled water. If that doesn't work, you might not have KNO3.
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post #3 of 14 (permalink) Old 09-11-2004, 03:18 AM
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If you don't need to use the solution immediately you can just dissolve the KNO3 in hot water. But I wouldn't recommend using hot tap water as there is concern that hot tap water is more likely to contain dissolved mineral from the water heater and pipes.

If you have it available, it may be better to nuke a cup of drinking water. But boiling cold tap water should be fine, too.

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post #4 of 14 (permalink) Old 09-11-2004, 09:23 AM
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Keep stirring!

You're not over the solubility level for KNO3 so it *will* all dissolve... I had to stir and stir to get 11.5 tsps to dissolve in 350ml of water.
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post #5 of 14 (permalink) Old 09-11-2004, 11:55 AM
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But the real question is why are you trying to make a solution? I find it's much easier to dose KNO3 dry.

What I do is pull a liter or so of water out of the tank, mix in my KNO3 and other nutrients, shake till dissolved and then pour back into the tank.
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post #6 of 14 (permalink) Old 09-11-2004, 12:25 PM
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Thats true. Dry dosing KNO3 is more convient especially since you have a larger tank - 66 gallons - well if you have a scale or very small measuring spoons. Just wondering though if you got your chemicals mixed up and you aren't trying to dissolve KNO3. Is that possible?

Get a small amount place it into a small flame. KNO3 should make the flame violet. Or you can make a very small mix of KNO3/sugar and ignite it outside. It should burn/flare up a lot. Do this on your own risk!! I am not responsible for any harm.
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post #7 of 14 (permalink) Old 09-11-2004, 01:03 PM
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Quote:
Originally Posted by Rex Grigg
What I do is pull a liter or so of water out of the tank, mix in my KNO3 and other nutrients, shake till dissolved and then pour back into the tank.
Thatís what I do as well. Very easy and straight forward except I punched a small hole in the bottom of a plastic cup to form a small stream so it doses over 3 minutes or so. Probably does not do anything I just thought it easier on the fish.

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post #8 of 14 (permalink) Old 09-11-2004, 06:25 PM
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I still dose in solution. I just use my pipettes and dose the aquarium. Seems like six of one and half a dozen of the other to me!

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post #9 of 14 (permalink) Old 09-11-2004, 06:49 PM
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Quote:
Originally Posted by Momotaro
...Seems like six of one and half a dozen of the other to me!
Same here. Either way, you're dissolving the ferts in water. I like to pre-dissolve and then dose with the solution.

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post #10 of 14 (permalink) Old 09-12-2004, 07:03 PM
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Add more water to the mix, try adding 10 ML at a time until it all dissolves. RO water is best for mixing since it has less dissolved minerals in it and will hold more of whatever you mix with it.
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post #11 of 14 (permalink) Old 09-13-2004, 03:29 PM
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Double the water and just add twice as much when dosing. If you go the adding the 10 ml's at a time route it's a pain to calculate exactly how much to dose.

I've gone all the way to customizing the concentration so that one eye dropper full will raise the NO3 1 ppm in my tank. (My eye dropper is not quite 3 ml's but it doesn't matter anymore.)
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post #12 of 14 (permalink) Old 09-13-2004, 04:16 PM
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I too only make a solution for phosphate and plantex. kno3 and k2so4 both get mixed in about 10 oz of tank water (i use a turkey baster to suck out the water into the mixing shaker).

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post #13 of 14 (permalink) Old 09-13-2004, 04:57 PM
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I agree that it probably just needed more stirring (KNO3 is VERY soluble) , but a point to make: for some solutes (including KNO3), dissolving is an endothermic process - the temperature of your solution will decrease as the compound dissolves. Solubility of solids decreases as temperature decreases. If you are making a concentrated solution for dosing you may need to either heat the water or wait for it to come back up to room temp to complete the dissolution process.

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post #14 of 14 (permalink) Old 09-13-2004, 06:52 PM
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Quote:
Originally Posted by amanda huggenkiss
Same here. Either way, you're dissolving the ferts in water. I like to pre-dissolve and then dose with the solution.
I agree. I simply make up my solution in a 500ml water bottle and dose from that every other day. It just takes some shaking to dissolve the KNO3 again. The more water you add and less KNO3 you add the easier it is to dissolve it.

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