Testing Concentration of Calcium Dosing Solution

[erk]

I'm having trouble keeping my Calcium level stable. I use ESV supplements and my LFS offers a discounted price for refills on the ESV alk, calc, and Mg supplements. I've refilled twice now and the refilled solution is what I'm dosing via autodoser. The tank is 25 gal. I thought it was just high consumption rate, but this doesn't explain the constantly increasing alk level even though I'm dosing calcium and alk in equal portions per the ESV instructions. I've even tried dosing 3:1 calcium solution to alk solution to try increasing calcium, and alk just continues to increase.(3:1 is 15ml Ca/5ml Alk)

This led me to questioning the concentration of the calcium solution. I diluted 1ml of calcium solution in 200ml of RODI. The label says 1ml per 3.8L will raise the calcium concentration 16ppm. 3800/200=19, so my diluted solution should be 19 times more concentrated. I wanted a calcium concentration of ~300ppm so my Red Sea test kit will pick it up. Now the questions:

-Did I dilute the right amount of calcium solution to achieve a concentration of 300ppm if the Ca solution is full strength?
-Can the Red Sea calcium test kit measure the calcium level in freshwater? If so, the concentration came to ~85ppm calcium.

I'm kind of hoping I did this wrong because I'm going to be pretty ticked off if my LFS sold me a solution that is only 1/3rd as potent as it should be.

For completeness, here are my alk, Ca, and Mg measurements:
Mg Alk Ca
2/15/2016 1360 | 8.7 | 400 <- Did a water change the day before to get levels in line
2/17/2016 1360 | 9.5 | 400

I dose 10ml of each part of the 2 part solution.

 

[JimWelsh]

I followed your math, and I calculate that the Ca concentration of your 1 mL calcium solution in 200 mL RO/DI should be 304 PPM based on the information you provided. Your reasoning is sound. EDTA titrations work equally well in both salt and fresh water.

 

[biom]

it is good to check now with 2 ml in 200ml RO water just to eliminate possibility that RS test kit is not working well in low ranges.

 

[erk]

I created a calcium solution from brightwell calcium chloride I had on hand. I dissolved ~135g in 1L of RODI to get a concentration close to what the ESV concentration should be. Diluted 1ml in 200ml and got 265ppm. I'll test again at 1.5ml tonight, but it's looking like my LFS screwed me. Glad I found this out before it crashed my tank.

Also, thanks everyone for your help.

 

[Randy Holmes-Farley Verified Community Expert]

Probably time for a new LFS.

 

[JimWelsh]

I created a calcium solution from brightwell calcium chloride I had on hand. I dissolved ~135g in 1L of RODI to get a concentration close to what the ESV concentration should be. Diluted 1ml in 200ml and got 265ppm.

Just to confirm: The solution you created here should have had 245 PPM Ca.

 

[erk]

Just to confirm: The solution you created here should have had 245 PPM Ca.

I added 95g to a 1L solution that contained ~40g of CaCl. It was probably more like 900mL of solution left, so this explains the 20ppm difference. Thank you so much for checking my numbers. Chemistry has never been my strong suit. Hence the reason I went to mechanical engineering.

Probably time for a new LFS.

Yes, I think you're right. Very disappointed. I think I'll buy the ESV solution from BRS or some other site from now on.

If anyone in the DFW area is wondering which LFS it is, please PM me and I will tell you privately.