Mixing Potassium Sulphate - The Planted Tank Forum
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post #1 of 24 (permalink) Old 03-30-2005, 10:21 AM Thread Starter
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Mixing Potassium Sulphate

Hello,

I got my K2SO4 yesterday, I used Chucks calculator and added 238grams of powder to 1900ml of water to give me .42ppm per ML.

Problem is the powder hasnt and wouldnt fully dissolve! The calculator said it would be fine...?

Will it dissolve over the coming days or am i left with some powder left in the bottom?

I tried mixing it and grinding it up against the jar but to no use.

therefore i doubt 1ML is .42ppm more like .3x or something...

I probably shouldnt have mixed up such a large stock solution now but it should keep shouldnt it?

I think I need to add 34ml a week which means the jar is going to last me 55 weeks!!

My KNO3 stock solution has lasted me over 10 months so far without problems.
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post #2 of 24 (permalink) Old 03-30-2005, 01:24 PM
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You are just above the solubility limit (1g K2SO4 per 8.3ml water = 238g in 1975ml). If the solution is colder, it will have even more trouble dissolving. The solubility also assumes you are using ion-free water - solubility is less when other ions are present.

You COULD assume you have a saturated solution (1 g in 8.3 ml is the same as 12g in 100ml) and still use it. It might be a little off (due to temp and presence of other ions), but still usable.

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post #3 of 24 (permalink) Old 03-30-2005, 01:40 PM Thread Starter
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I'll try adding an extra 100ml with hot water and try warming up the solution...

see if i can dissolve it all then!

do you know how long the stock solution will last?
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post #4 of 24 (permalink) Old 03-30-2005, 02:21 PM
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Lightbulb

I bought and use one of these:

http://www.coleparmer.com/catalog/pr...=1&sel=8400000

http://www.coleparmer.com/catalog/pr...=1&sel=0477598

It's probably one of the best investments I've made... I use it all the time.
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post #5 of 24 (permalink) Old 03-30-2005, 04:09 PM
 
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I just does it dry straight into the tank.
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post #6 of 24 (permalink) Old 03-30-2005, 04:10 PM
 
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Sorry... *dose*!
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post #7 of 24 (permalink) Old 03-30-2005, 05:48 PM
 
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Yeah, no sense in making a solution, just dry dose it. Only thing you really need to make solutions of is Phosphate (from KPO4) or if you use Plantex for your trace. Everything else can be dry dosed.

As it stands you're going to have to add 40 mL of your solution to hit the typical 20ppm of potassium in your tank. That's far from convenient.
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post #8 of 24 (permalink) Old 03-30-2005, 07:50 PM
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I mix 1 tsp in a cup then dump it in my tank.

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post #9 of 24 (permalink) Old 03-30-2005, 09:08 PM Thread Starter
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wish I knew this before hand!!! oh well.... i'll just add the required ML's until it runs out the dry dose.
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post #10 of 24 (permalink) Old 03-31-2005, 02:56 AM
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If you just "dump it in," how is it dissolving? It just seems to me that it's going to sink to the bottom and a good portion of what you dosed will settle in the substrate.
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post #11 of 24 (permalink) Old 03-31-2005, 09:20 AM
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Quote:
Originally Posted by Hypancistrus
If you just "dump it in," how is it dissolving? It just seems to me that it's going to sink to the bottom and a good portion of what you dosed will settle in the substrate.
Depends how fine the powder is, how much you are dosing in one go, strength of water current, temperature of the water, and probably, the tds value of your tank water.

I have tried dry dosing, and I feel that for me it isn't practical as I find it takes a few seconds for the substance to dissolve and I don't want that near my curious fish!

The best thing to do if dry dosing is to try and get the powder as fine as possible and to put little bits in at a time, slowly and directly into the path of the filter outflow, so it gets immediately mixed round the tank. Once happy it's dissolved, add some more and so on.

Personally, I find it easier to pre-mix the dose, not as a stock solution, but with a little tank water to get it initially dissolved into a concentrated solution, which is then completely added to the tank.
This works for me as I weigh the compound directly into a small bottle on my scales, then add the water, shake up (in same bottle) and I'm done, ready to dose into the tank.

My tanks are relatively "small" (see signature), so this remains pratical for my situation.
I use.....
99.9% pure, ball milled KNO3 which is excellent at dissolving.
99.9% pure KH2PO4, which is good at dissolving, but could be ground a bit further into fine powder.
Commercial, off-the-shelf Sulphate of Potash, which is a pain to dissolve, partly due to the amount I add, but also because it is far from "fine" and contains irregular lumps of compound, which if not careful and get into the tank, will remain on the tank floor (waiting for a hungry inquisitive fish!).

Moral is; you pay for what you get basically. If you want to make life easiest, go for the 99.9% pure, fine powdered versions of compounds. (which I think is what Greg Watson sells )

Whilst I prefer the quick pre-mix option for my tanks, I by no means state this is better than any other method. Do what works for you and your situation..... ignore the "do this" opinions, it's a process of learning.
If you have many tanks, it's probably better to make a standard stock solution to which you dose to all tanks in different amounts.
If you have one large tank, which occasionally gets dosed, dry dosing would probably be better.

HTH


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post #12 of 24 (permalink) Old 03-31-2005, 12:49 PM
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I use Greg Watson's K2SO4 and other K, and I just dry dose them- they dissolve right away.

30g planted with cories, white clouds, Harlequin Rasboras ,ottos.
10g planted with glowlight tetras and an otto.
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post #13 of 24 (permalink) Old 03-31-2005, 01:56 PM
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Does 1/2 tsp potassium 3x per week in a 37 gallon with 3.25 wpg and co2 above 30ppm sound like too much? I'm flying through my bag of it and was wondering. I also dose kno3.

40 gallon SeaClear Acrylic, 192 watt Orbit Lunar PC, Filstar XP2, Filstar XP1, JBJ Regulator, Rhinox 5000 glass co2 diffusor, 9 watt UV sterilizer, Hydor Inline Heater, Pool Filter Sand substrate
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post #14 of 24 (permalink) Old 03-31-2005, 03:39 PM
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Quote:
Originally Posted by Anthony
Does 1/2 tsp potassium 3x per week in a 37 gallon with 3.25 wpg and co2 above 30ppm sound like too much? I'm flying through my bag of it and was wondering. I also dose kno3.
I make that about 11.8ppm of Potassium each time you dose (without taking into acount any K from KNO3 or KH2PO4).

K2SO4 is the compound everyone goes through the quickest.


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post #15 of 24 (permalink) Old 03-31-2005, 05:18 PM
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Quote:
Originally Posted by Hypancistrus
I bought and use one of these:

http://www.coleparmer.com/catalog/pr...=1&sel=8400000

http://www.coleparmer.com/catalog/pr...=1&sel=0477598

It's probably one of the best investments I've made... I use it all the time.
eek gads. $260? A bit pricey for a glorified stir.

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