Ca imbalance/test kit issue? Questions?!

[wade1]

This is in the main reefs.org discussion forum, but I thought it might get more attention here:
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A couple of months ago, I made a mistake and added CaCl2 to my tank instead of an alk booster (Reef Builder). I added enough to shoot my Ca sky high. Here is what I have found:

4/17 - Ca 825 alk 10.2
4/26 - Ca 890 alk 10.5
5/5 - Ca 900+ alk 10.8

I am running a reactor at around 150ml/min with an effluent pH around 6.9. I have added no chemicals to the tank since and have done two 15% water changes. I will test again today and see where the levels are (since I changed the second 15% last night), but here are the questions:

Is 900ppm Ca truly above saturation in seawater at 81F? If so, what else could be interfering with the test kit reading? I have used 2 different sources of RO/DI water and tested them both with no measurable exogenous Ca. I have used 2 different kits, from different lot numbers, both Lamotte brand. Both give the same results.

Could it be another divalent metal interfering? Something else?

I am getting extremely good growth on my sps (my acros are outgrowing my montiporas) and the soft corals and fish (even the powder blue tang) have no visible signs of stress. The sandbed is not cementing and I am seeing no precipitation in the tank. Sg is at 1.025. Temp is 79.5-83F.

Anyone have any thoughts, suggestions, or possibilities?

Thanks!
Wade

 

[randy holmes-farley]

Is 900ppm Ca truly above saturation in seawater at 81F?

Yes, but then again, so is 200 ppm. Natural seawater is substantially supersaturated already. If you really have 900 ppm, then have just pushed it to more extreme levels.

Anyone have any thoughts, suggestions, or possibilities?

It could be a real calcium level, or it may be a faulty reading. Are you sure it is reading in ppm of Ca++ and not ppm of CaCO3 (the Hach kit reads this way)?

If it is a real Ca++ reading in ppm, then I'd add an alkalinity supplement and back off on the reactor until the Ca++ level declined.

More likely, it is a faulty reading or interpretation, and no action is required except getting a verified reading.