help understanding Ca/Alk numbers

[das75]

Have a reactor that was going fine until I decided for a higher Ca and ended up maxing out my alk levels. Turned off the CO2 and figured would be doing a water change but alk is dropping pretty good on it's own.

Because of the fast drop in alk, wondering if I got other problems?

Mar 11 Ca 400, alk 14, noted but left town
Mar 16 Ca 400, alk 15, returned, CO2 off
Mar19 Ca 390, alk 11.2

Test kits Salifert, use IO salt, no supplements other than the Seachem Reef Ca I added about a week ago to help bring up the calcium.

Tank is 145g, basically would say lightly stocked on the SPS side, mutant growing xenia, couple LPS, zoos and a 5" Crocea.

 

[jdieck]

I think you know by now that you can not increase Calcium with a reactor without increasing Alkalinity.
Your plan is OK, just keep the CO2 off until the alkalinity is down to 10 dKh and keep supplementing Calcium to maintain it at 420 using the Sachem Advantage Calcium.
Once Alklainity is at 10 and Calcium at 420 you can restart the CO2, I will suggest a bubblewrate that maintains your alkalinity.
If in the future you need to adjust Calcium only then just use the Calcium supplement. No need to turn off the reactor to supplement only Calcium.
You can use the Chemistry calculator to determine how much Calcium supplement you need to add to reach your target.
http://home.comcast.net/~jdieck1/chem_calc3.html

 

[das75]

Had been keeping the tank fairly steady before at Ca 350ppm/alk 10KH at an effluent rate of 40drops/min and 20 BPM. Alk rise started when I changed to 60ml/min and 40 BPM so will be going back to previous rate as start point.

Is a drop of more than 1KH/day normal if not supplementing?

 

[jdieck]

Yes go back to the effluent and CO2 rates you had when maintaining a steady alkalinity.
If necesary keep supplementing with the Seachem Reef Calcium if it is still low, again adjust to maintain the alkalinity constant and dose to adjust Calcium, once adjusted the calcium will stay on target. Also keep in mind to maintain your Magnesium at the proper level (1300 ppm) and supplement if needed.