False Calcium Test Results?

[Midrats]

I added some Tropic Eden Aragasnow to my tank. It's a sugar-sized aragonite sand. Since then my calcium readings have been >500 on my Salifert kit. I haven't noticed any anomalies with my alkalinity. I discontinued limewater for a couple of days then tested. The calcium was still >500 and the alkalinity had fallen as expected so I have resumed limewater additions. The water is crystal clear. How long can I expect this interference with my calcium testing?

 

[GoVols]

Tagging

 

[Randy Holmes-Farley]

I added some Tropic Eden Aragasnow to my tank. It's a sugar-sized aragonite sand. Since then my calcium readings have been >500 on my Salifert kit. I haven't noticed any anomalies with my alkalinity. I discontinued limewater for a couple of days then tested. The calcium was still >500 and the alkalinity had fallen as expected so I have resumed limewater additions. The water is crystal clear. How long can I expect this interference with my calcium testing?

How are you measuring alkalinity?

I do not know why your calcium rose, but the aragonite is not likely interfering. If it was in suspension (in which case it may show up), it will show up very much in an alkalinity test. Each 20 ppm calcium boost from suspended aragonite would show up as an extra 2.8 dKH of alkalinity.

 

[Larry L]

I'm not sure those are false results. Aragonite (which is calcium carbonate) supposedly buffers around 8.2 pH, so if your pH was lower than that when you added the aragonite, I think some of it would have dissolved and released calcium.

 

[Randy Holmes-Farley]

I'm not sure those are false results. Aragonite (which is calcium carbonate) supposedly buffers around 8.2 pH, so if your pH was lower than that when you added the aragonite, I think some of it would have dissolved and released calcium.

The pH needs to be well down into the 7's, and besides, it boosts alk a lot when it dissolves.

 

[Larry L]

The pH needs to be well down into the 7's, and besides, it boosts alk a lot when it dissolves.

Thanks Randy, I overlooked the part where the OP said "haven't noticed any anomalies with my alkalinity".

 

[Midrats]

How are you measuring alkalinity?

I do not know why your calcium rose, but the aragonite is not likely interfering. If it was in suspension (in which case it may show up), it will show up very much in an alkalinity test. Each 20 ppm calcium boost from suspended aragonite would show up as an extra 2.8 dKH of alkalinity.

I'm using a Hanna alkalinity colorimeter. It has always been pretty consistent. I don't think the calcium is much over 500 because I only needed to add a few more drops beyond the 1 ml to get the color change. Admittedly I don't monitor calcium that closely and haven't tested it in a while. I just thought that I had read somewhere that suspended aragonite fines can give false test results. I suppose if my alkalinity is in check I can assume the calcium results are correct.

 

[Randy Holmes-Farley]

I'm using a Hanna alkalinity colorimeter. It has always been pretty consistent. I don't think the calcium is much over 500 because I only needed to add a few more drops beyond the 1 ml to get the color change. Admittedly I don't monitor calcium that closely and haven't tested it in a while. I just thought that I had read somewhere that suspended aragonite fines can give false test results. I suppose if my alkalinity is in check I can assume the calcium results are correct.

You are right it does give false readings, just not to only calcium. I’d just ignore the issue for a while and keep watching calcium over time. [emoji3]