Dosing confusion

DonF · Feb 24, 2020

Hi, we bought Red Sea Foundations test and dosing kits. Our Kh and Mg levels were low, and so we used an online calculator recommended by our LFS to figure out how much to dose. Well, it seems it was way off for Mg! According to the calculator (I double checked against a different one, too) it should have taken 560ml of the Mg product to reach our target. We were planning on 30ml per day. Well, 24hrs after dosing 30ml our Mg level went from 1080 to 1600ppm.

Similarly, we planned to raise Kh over two days. After the 1st 16ml dose we’re up to 7 dKh from 6.4, which seems reasonable.

How did Mg shoot up after just one dose?

Now that we have reasonable numbers, how can we figure out the right daily does to maintain? Between the display and sump we’re at about 40 gallons.

Current #’s

Ca 480
Mg 1600
Kh 7

All other parameters are good, too.

GoVols · Feb 25, 2020

DonF said:
Hi, we bought Red Sea Foundations test and dosing kits. Our Kh and Mg levels were low, and so we used an online calculator recommended by our LFS to figure out how much to dose. Well, it seems it was way off for Mg! According to the calculator (I double checked against a different one, too) it should have taken 560ml of the Mg product to reach our target. We were planning on 30ml per day. Well, 24hrs after dosing 30ml our Mg level went from 1080 to 1600ppm.

Similarly, we planned to raise Kh over two days. After the 1st 16ml dose we’re up to 7 dKh from 6.4, which seems reasonable.

How did Mg shoot up after just one dose?

Now that we have reasonable numbers, how can we figure out the right daily does to maintain? Between the display and sump we’re at about 40 gallons.

Current #’s

Ca 480
Mg 1600
Kh 7

All other parameters are good, too.

If the calculator is right???

You dose to the actual water that your holding, not the tank size.

I'm rated at 110 gallons, but really holding 80 gallons after displacement of things like live rock.

Next time dose to a smaller gallon size, and move up, until you know how many gallons that your really holding.

Randy Holmes-Farley · Feb 25, 2020

That calculator is accurate. Many years of experience has shown that tests and reefer entries to it often are not.

Randy Holmes-Farley · Feb 25, 2020

The Red Sea magnesium kit is notoriously problematic in ordinary hobbyist hands.

DonF · Feb 26, 2020

GoVols said:
If the calculator is right???

You dose to the actual water that your holding, not the tank size.

I'm rated at 110 gallons, but really holding 80 gallons after displacement of things like live rock.

Next time dose to a smaller gallon size, and move up, until you know how many gallons that your really holding.

I tried to account for displacement, and couldn’t be off enough to account for what I saw - i.e. that 5% of the recommended dose brought me from 1080 to 1600.

I looked at several calculators and they all give me the same numbers.

My conclusion, at this point, is that I must have done a bad initial test. The 1080 number must have been wrong, in other words.

homer1475 · Feb 26, 2020

DonF said:
My conclusion, at this point, is that I must have done a bad initial test. The 1080 number must have been wrong, in other words.

This would be my guess, or you dosed to the wrong volume.

For instance, I have an 80G display with 30G sump, or 110G total. But I don't fill my sump to the top, and I have rock and sand. Through time, and using calcs, I have found out I really only have 83G of water.

With that said, did you account for displacement?

DonF · Feb 26, 2020

homer1475 said:
This would be my guess, or you dosed to the wrong volume.

For instance, I have an 80G display with 30G sump, or 110G total. But I don't fill my sump to the top, and I have rock and sand. Through time, and using calcs, I have found out I really only have 83G of water.

With that said, did you account for displacement?

I took a guess at displacement, but nothing scientific.

I’m going to test every day for a week to see how these numbers change. Hopefully I can then figure out depletion rate, and then come up with a daily dosing regimen. (Hopefully I also get good with the titration technique needed to get accurate numbers! Practice makes perfect, right?)