adding calcium to auto top off tank

[jakano]

hi randy i am sorry if this question has been asked before but the search functon is down. i use a 20 gallon aquarium that sits beside my 110 gallon reef to hold freshwater for top offs. i use a float switch to control the water level that changes do to evaporation . would there be any problems if i added your calcium recipe directly to this freshwater so that when it refills the sump it also adds the calcium the tank needs. i am sure i need to find a balcance in this which would be the problem i suppose. i am guessing the answer would be no since the evaporation probably doesnt happen at an even rate everyday. is there another suggestion you could provide that would work something like i had in mind. i am using the salifert all in one now and although it works pretty good is getting expensive but i love the ease of use it provides. i figured though that if i already have fresh water pumping in daily i could also use it to provide calcium that way as well. thanks for any info you can provide. oh i guess i should mention my tank inhabitants my tank has mostly lps corals with a couple of softies and one sps. in the future i do plan on adding more montipora to grow on my overflow as well.

 

[Randy Holmes-Farley]

IMO, you can add either the calcium or the alkalinity part (not both) to the top off water, and it should be fine. There will be more some days and less some others, but it will balance out as long as you add an appropriate amount, and adjust it as evaporation changes through the seasons.
I would be more inclined to add the alkalinity part that way, and then just add calcium once or twice a week (in an appropriate amount to balance the alkalinity that was added). I'd prefer the alk part because it drops more (percentage wise) on a daily basis, and it is easier to add a lot of calcium at once than alkalinity (since there is no pH effect from the calcium).