New test kit, very different result

[Pennywise the Clown]

My Salifert Calcium test kit had run out of reagent so I purchased a new one today (Salifert) The last test that I did 4 days ago showed my calcium level to be slightly lower than I would have liked at 400 so I upped my dose slightly by 2ml a day.

The new test kit has just measured Ca at 480. There is no way the extra 2ml a day has made that amount of difference and I was actually expecting to have to raise my dose more as my SPS frags are starting to show good signs of growth.

Both test kits have years left on them and now I'm not sure which one to trust.

 

[Crabs McJones]

Does your LFS do testing? Might not hurt to take a sample to them and see what they come up with and match it to your results. Or a reefer that lives close to you.

 

[Surfandturf]

If I get wildly different results, then I test twice. The reading may be correct. That extra 2 mls per day could be replacing what was being absorbed before. Did you do a water change before you tested again? There are always pumped up calcium levels in salt mix. 480 calcium is not a bad thing in my opinion.

 

[Pennywise the Clown]

If I get wildly different results, then I test twice. The reading may be correct. That extra 2 mls per day could be replacing what was being absorbed before. Did you do a water change before you tested again? There are always pumped up calcium levels in salt mix. 480 calcium is not a bad thing in my opinion.

I have done a water change between tests, only 15%, using Red Sea Blue Bucket. That usually mixes to 430 at 35ppt.
I've just tested my alk and that is holding steady at my usual 8.0.
I will test Ca again and see what I get.

 

[Pennywise the Clown]

Does your LFS do testing? Might not hurt to take a sample to them and see what they come up with and match it to your results. Or a reefer that lives close to you.

Unfortunately I would trust any LFS near me to test tap water.

 

[WVNed]

If you did a water change between the two tests I am not sure there is actually a problem

 

[Randy Holmes-Farley]

If you did a water change between the two tests I am not sure there is actually a problem

the problem is that calcium wouldn’t rise to that level. For a 15% change to boost calcium by 80 ppm, the new water would need to have calcium over 900 ppm.

 

[Pennywise the Clown]

I've done 3 calcium tests with the new Salifert test kit and got the same results every time.
I've tested with my old kit, apart from the titration solution which had run out, and got the same result (480)
My conclusion is that either my calcium level is indeed 480 or that the titration solution of the new kit is different.
I find it strange that I am having to up my alk, also having to dose magnesium for the first time (water changes aren't keeping up any more) and having to lower my calcium dose which isn't exactly high in the first place.