Potassium Depletion and Two Part Usage

Randy Holmes-Farley · Oct 1, 2015

Thanks for the info so far folks!

Randy Holmes-Farley · Oct 2, 2015

biom said:
Randy, can you calculate please how much KCl i should add to my Ca/MgCl2 mix (Real Two part ) to compensate K ion displacement. And i'll report back in a month or so after, if there is still K depletion..

OK, I ran the calculation. Add about 13 grams of potassium chloride for each 500 grams of calcium chloride dihydrate in a two part. Add it to either part, or both (half in each part).

biom said:
I I believe there will be because im dosing carbon and probably part of potassium is exported by skimmer together with bacteria. You know some strains of bacteria are capable to accumulate potassium 1000x more than concentration in surrounding water.
.

Not 1000x in seawater. That would be 10.2 M, which I doubt any organisms had internally of any salt (or all added together). They'd probably explode from the osmotic pressure.

But I agree they will concentrate it. OTOH, the foods we feed should also be concentrating potassium relative to seawater.

biom · Oct 2, 2015

Randy Holmes-Farley said:
OK, I ran the calculation. Add about 13 grams of potassium chloride for each 500 grams of calcium chloride dihydrate in a two part. Add it to either part, or both (half in each part).

Thank you very much, next time will mix with 13 grams KCl, currently there are 26 grams in 500 grams CaCl2*2H2O (calculated according consumption from previous two months).

Randy Holmes-Farley said:
Not 1000x in seawater. That would be 10.2 M, which I doubt any organisms had internally of any salt (or all added together). They'd probably explode from the osmotic pressure. But I agree they will concentrate it. OTOH, the foods we feed should also be concentrating potassium relative to seawater.

Yes, I believe 1000x was found in halophilic bacteria, in E.coli in sea water, potassium concentration could be up to 3-20x or so.

Randy Holmes-Farley · Oct 2, 2015

biom said:
Thank you very much, next time will mix with 13 grams KCl, currently there are 26 grams in 500 grams CaCl2*2H2O (calculated according consumption from previous two months).
.

If 26 grams meets your depletion rate, there's no reason to add less. My calculation assumes no net consumption in the tank, just displacement when you maintain salinity and are adding sodium, chloride, and sulfate.

biom · Oct 2, 2015

Yes, but i'm not sure if my calculated depletion rate is correct, you know hobby tests are pretty inaccurate. So i'll test for about a month mix with 26 grams and if it is to much will try 13 gr.

Randy Holmes-Farley · Oct 2, 2015

Sounds good.

Happy Reefing.

sonnus · Oct 3, 2015

Here's a recent AWT test of my tank. About 1 year ago the tank got a 100% water change so this represents 1 year of potassium depletion. The daily ALK consumption is about 1.5 dKH and the tank gets about 10% water change about twice per month. The calcium/alkalinity is maintained with a calcium reactor and 2-part dosing. I would say they equally contribute to the alkalinity dosing. Lately I've been using the Tropic Marin 3-part dosing but BRS 2-part was used the majority of time.

Randy Holmes-Farley · Oct 3, 2015

sonnus said:
Here's a recent AWT test of my tank. About 1 year ago the tank got a 100% water change so this represents 1 year of potassium depletion. The daily ALK consumption is about 1.5 dKH and the tank gets about 10% water change about twice per month. The calcium/alkalinity is maintained with a calcium reactor and 2-part dosing. I would say they equally contribute to the alkalinity dosing. Lately I've been using the Tropic Marin 3-part dosing but BRS 2-part was used the majority of time.

FWIW, I would be wary of the AWT potassium number. They have a long history of seemingly giving low values. I'd double check it a different way before dosing that much potassium.

They fact they they give different values for ionic and total calcium is also troubling, since it is essentially all ionic in seawater.

jcdeng · Oct 3, 2015

what is a good potassium test kit?

sonnus · Oct 3, 2015

Randy Holmes-Farley said:
FWIW, I would be wary of the AWT potassium number. They have a long history of seemingly giving low values. I'd double check it a different way before dosing that much potassium.

They fact they they give different values for ionic and total calcium is also troubling, since it is essentially all ionic in seawater.

Good to know. Thanks

ohioboy706 · Oct 4, 2015

I would like to know a good potassium test too. I have a Salifert test that is close to running out and been on a waiting list for almost a yr.

Randy Holmes-Farley · Oct 4, 2015

I've not used any lately. When I tested a few years ago with the Fauna Marin, my tank did not appear depleted. When I got Triton tested a few months ago, that confirmed that it isn't depleted. So I've not used any kits recently.

I've seen some people have preferences between the Salifert, Red Sea and Fauna Marin potassium kits, but I've not seen a consistent trend in opinions on them, and I've not seen an accuracy evaluation of any of them.

biom · Oct 15, 2015

Update from my potassium experiment 14 days after. I put 26 grams KCl in 500 grams calcium part (CaCl2*2H2O), my potassium was 370 ppm (Salifert) in the beginning and is 360 ppm 14 days after. No water changes in between. I've calculated more than 1.1 ppm K consumption per day. Having in mind Salifert's test accuracy 10 ppm, i'd wait another two weeks prior final calculation.

Randy Holmes-Farley · Oct 15, 2015

Sounds good. Thanks for the update.

biom · Dec 13, 2015

update, 70 days after, average Potassium consumption in my tank is 2.53 ppm per day.

Unfortunately finished Salifert Potassium test, @Habib(Salifert) Habib you promised mid of November

? @Randy Holmes-Farley , @JimWelsh do we have good/any DIY test for potassium

?

Randy Holmes-Farley · Dec 13, 2015

biom said:
update, 70 days after, average Potassium consumption in my tank is 2.53 ppm per day.

Unfortunately finished Salifert Potassium test, @Habib(Salifert) Habib you promised mid of November ? @Randy Holmes-Farley , @JimWelsh do we have good/any DIY test for potassium?