The Planted Tank Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
51 Posts
Discussion Starter · #1 ·
I’m having some issues getting one of the ferts in my macro mix to dissolve and I suspect it’s the K2SO4.

I’m using KNO3, KH2PO4 and K2SO4 plus a little ascorbic acid to acidity the solution.

Today I mixed 90g K2SO4 into 1000ml water with about 20g of KNO3 and KH2PO4 and was left with a white substance consisting of many small white “balls”. With a little heat and lots of time on the magnetic stirrer they eventually dissolved.

Anyone else have a similar experience?
 

·
Registered
Joined
·
621 Posts
I’m having some issues getting one of the ferts in my macro mix to dissolve and I suspect it’s the K2SO4.

I’m using KNO3, KH2PO4 and K2SO4 plus a little ascorbic acid to acidity the solution.

Today I mixed 90g K2SO4 into 1000ml water with about 20g of KNO3 and KH2PO4 and was left with a white substance consisting of many small white “balls”. With a little heat and lots of time on the magnetic stirrer they eventually dissolved.

Anyone else have a similar experience?
Yes, my K2SO4 takes it's time to dissolve when I put it in the tank. It lands on the leaves and just stays there a while. I don't have any fish. A fish might try to catch it as it falls. But that's not why I don't have any fish. I like how you're making a dosing solution. It's such an effective way to dose. It can be really accurate too.
 

·
Registered
Joined
·
500 Posts
I’m having some issues getting one of the ferts in my macro mix to dissolve and I suspect it’s the K2SO4.

I’m using KNO3, KH2PO4 and K2SO4 plus a little ascorbic acid to acidity the solution.

Today I mixed 90g K2SO4 into 1000ml water with about 20g of KNO3 and KH2PO4 and was left with a white substance consisting of many small white “balls”. With a little heat and lots of time on the magnetic stirrer they eventually dissolved.

Anyone else have a similar experience?
It seems like you are adding alot of K?

According to rotalabutterfly.com the solubility of K at room temperature is around 120 gm. Add up all additions and that might be the culprit?

Sent from my Pixel 3 XL using Tapatalk
 

·
Registered
Joined
·
93 Posts
Yes, K will put you over the top everytime. I now add a mass dose of K alone after every water change. So per water change I add around 15ppm of K, the rest of my dose comes from the addition of NO3 and PO4 throughout the week.
 

·
Registered
Joined
·
51 Posts
Discussion Starter · #5 ·
It seems like you are adding alot of K?
Not a huge amount. But NO3 dosing is relatively lean, so it's basically all composed of K2SO4. KH2PO4 doesn't contribute a whole lot. I've also found the solution cools a little with the addition of one of the compounds, so I suspect the solubility is even less than 120g/L at the time I'm mixing. An endothermic reaction (if my high school days don't betray me) seems to be going on somewhere.

And thanks everyone, glad to see it's not an uncommon issue.
 

·
Registered
Joined
·
49 Posts
KNO3 has an endothermic dissolution, so it is the one that causes the cooling. I have some experience making saturated solutions of some salts, such as NaCl and NaHCO3 and they also take some time to dissolve when approaching the saturation point. Glucose is even worse. I would just let it stir with the magnetic bar for as long as it is needed (just like you are already doing).
 
1 - 6 of 6 Posts
Top