Very uneven calc/alk dosing

timnem70 · Feb 6, 2018

Also. Chasing numbers that small is gonna drive ya nuts. If Alk stays constant, that is between 8.5 and 9.0dkh chasing a 390 to 410 calcium number is really insignificant. I think I hear you saying though that you're just looking to see what's actually using it?
Is thay my understanding? Forgive if not. Dont worry about your calcium. It is in range. What is your Magnesium level? That will undoubtedly affect your Other two.
I hope you get it squared away.

TheEngineer · Feb 6, 2018

You're right. I'm not worried about the value, just wondering where the additives are going because I'm not seeing the change I'd expect. I haven't checked mag in forever. I can check it.

Randy Holmes-Farley · Feb 6, 2018

TheEngineer said:
I have a lot less faith in the hanna calc test too. It's 100:1 in terms of sample to water volume and that concerns me.

yes, and that huge multiplier on the blank causes issues if the blank water is not totally pristine.

Randy Holmes-Farley · Feb 6, 2018

TheEngineer said:
You're right. I'm not worried about the value, just wondering where the additives are going because I'm not seeing the change I'd expect. I haven't checked mag in forever. I can check it.

If the actual alk depletion is what you say (0.06 dKH per day), you'll never detect the magnesium depletion relative to the salt mix. It would be on the order of 0.02 ppm per day.

Brew12 · Feb 6, 2018

I like the idea of measuring how much you are dosing over 24 hours as a check. That is probably a good habit to get into every few months.

If it were me, I would stop dosing everything for 2 or 3 days. Use the Redsea kits to test Alk and Calc at the same time each day. This way you can determine the actual current alk/calc consumption of your tank and then start dosing accordingly.

TheEngineer · Feb 6, 2018

Mag is at 1260. Slightly low but within range.

I like that idea. Im out of town tomorrow so I won’t catch it in time. I’ll plan to do it Thursday.

TheEngineer · Feb 8, 2018

Just checked the dosage for the last 24 hours. I'm assuming some evaporation, esp with how little gets dosed at a time. I measure a little under 2mL, around 1.75mL. So at least I know the doser it performing as expected.

I didn't dose alk or calc yesterday. I'll measure both here shortly using Red Sea for calc and Hanna for alk.

Randy Holmes-Farley · Feb 8, 2018

TheEngineer said:
Just checked the dosage for the last 24 hours. I'm assuming some evaporation, esp with how little gets dosed at a time. I measure a little under 2mL, around 1.75mL. So at least I know the doser it performing as expected.

I didn't dose alk or calc yesterday. I'll measure both here shortly using Red Sea for calc and Hanna for alk.

At the dose you are using, even with no dosing, you won't see an alk decline in less than a few days.

TheEngineer · Feb 8, 2018

Red Sea Alk: 8.7 (same as it was yesterday when I pulled the doser)
Red Sea Calc: 370 (same as it was two days ago)

Now I'm going to add 150mL of two part. That should bump me up to 400 ppm, well within the 50ppm per day max increase but noticeable on a test.

TheEngineer · Feb 8, 2018

Made a quick “doser”

TheEngineer · Feb 8, 2018

Annnnnd now I'm at 420ppm.... WHY!?

I did the test 2 times. I might be off on my water volume, but not by a factor of almost 2.

Randy Holmes-Farley · Feb 8, 2018

Our kits are not perfect, either is our measurement of tank water volume, etc.

TheEngineer · Feb 8, 2018

But how can this be? I tested twice at 370 and twice at 420. It should take 150mL to increase by 30ppm. Instead I went up 50ppm which should have taken 250mL. That’s a substantial difference.

Brew12 · Feb 8, 2018

TheEngineer said:
But how can this be? I tested twice at 370 and twice at 420. It should take 150mL to increase by 30ppm. Instead I went up 50ppm which should have taken 250mL. That’s a substantial difference.

Unfortunately, it isn't that hard to believe. A Redsea Calc test kit has a best case accuracy of +or-5ppm. When comparing 2 points it is possible to be up to a total of 20ppm off. That alone could make up the difference and that using the kit absolutely perfectly. Add in the fact that you may not have a perfect mix of 2 part, non exact tank volume, and less than perfect test kit usage and being 20ppm off isn't surprising.

This is one reason I feel it is very important to do your tests exactly the same way each time. Go for stability and comparability, not accuracy.