Mg/K Dilution

[BenB]

GH here is < 1. What little GH I have is composed of Ca. So I'm trying to make a Mg/K dilution. I add Ca, Mg, and K after a water change, but I want to top up a little bit maybe half way to the next water change.

I have an ADA 60p. Volume is about 17gal. I made a dilution such that 15ml gave me 5ppm Mg and 10ppm K. In 500ml it was 108.8gm MgSO4 and 47.8gm K2SO4.

The mixture still has a bit of dust in it, but I'm wondering if it just isn't impurities because the water also turned very slightly brownish.

Anything thoughts? I can always dry dose, but doing this eliminates a couple maintenance steps and saves time.

 

[Marwen]

If it's just a small bit, it could be impurities. You could filter them out with a coffee filter if you don't want to see them or are worried about them going into some dosing pumps.

If it's a very fine white cloudy/milky dust that takes a while to settle down fully, and you used water that contains some calcium, then it's most probably CaSO4. When you add enough SO4 (in your case you have quite a lot from K2SO4 and MgSO4) and enough Ca to a solution, they can easily form CaSO4 precipitate because the latter has very low solubility (maximum 1.3 g per your 500 mL, anything more will form undissolved CaSO4 powder). For your use, this is completely harmless.

If it looks more like grains of table salt that settle readily at the bottom, then it's probably undissolved K2SO4. It's already kind of a PITA to dissolve, plus you are almost at its solubility limit with that concentration. Three options in this case:

1. Heat up the solution in the microwave (no boiling) and stir until finally dissolved.
2. If that doesn't work, top up the solution with water until its 666 mL instead of 500 mL (and use a 20 mL dose instead of 15 mL). Heat up and try to dissolve.
3. Ignore it and accept having a little bit less K per dose.

Hope that helps.

 

[BenB]

Yeah, its just a wisp of powder that scatters when I barely touch the container. I had thought about the coffee filter thing, but I don't have any. It's not worth it to buy it.

If it's a very fine white cloudy/milky dust that takes a while to settle down fully, and you used water that contains some calcium.

And this could potentially be it. I used tap water because it has a really low in TDS. I've watered carnivorous plants with it, and they don't tolerate any salts in the water. However, when making a very concentrated solution, I might have hit that wall, whereas just mixing a few micros or more dilute solutions wouldn't cause an issue.

1. Heat up the solution in the microwave (no boiling) and stir until finally dissolved.

Yeah, already tried that one, and it didn't work.

1. If that doesn't work, top up the solution with water until its 666 mL instead of 500 mL (and use a 20 mL dose instead of 15 mL). Heat up and try to dissolve.

I might try this just out of curiosity. There is so little, if it is the low solubility of the K, I bet the extra volume will be enough to work.

1. Ignore it and accept having a little bit less K per dose.

Ha! Was already leaning on this one. Honestly, I'm not sure I need the extra Mg or K, but my tank has been looking great. So I'm inclined to stick with the plan.

Hope that helps.

Oh definitely. Thanks!

 

[BenB]

I added a bit more distilled water to my dilution. I had a chance to look at it today in better light.

The precipitate was still there and some was definitely brown. I'm leaning on it being impurities, but I'm curious to remake it with only distilled water to see if it happens again. If it still does, then I know it is impurities. If it doesn't then, CaSO4.

I'll see about it this weekend.