Importance of a Calcium Reactor?


New member
How important is a calcium reactor to a large system?
I am setting up an 900 gallon total system and am planning on using fresh Ocean water with 20% water changes every 2 weeks
so would a Calcium Reactor be absolutly needed?
The set up would consist of a mixed reef with some SPS but more focus on soft corals some clams and anemones.
Importance or cost factor?

You can use two-part to maintain the alk and calcium but it would cost you a lot more than using a calcium reactor. Depending on the consumption using kalk water may work but is limited to your evaporation rate. Kalk water is cheaper than two-part, but more expensive than a calcium reactor once your purchase the equipment. The biggest draw-back when using a calcium reactor is the initial cost and some reduction of tank pH. ;)

Randy compares the costs of operation using the various methods to maintain your calcium and alk levels in this article:

How to Select a Calcium and Alkalinity Supplementation Scheme


New member
wouldnt the every 2 weeks 20% water change with real ocean water maintain the Calcium and Alk level sufficient?
Seawater averages an alk level of around 7 dKH. So it's not going to really add much deficit alk since you want to maintain at least 7 dKH perhaps a bit higher. The same is true for calcium.


Premium Member
Many tanks consume 2-3 dKH per day. :) Water changes can't keep up very well with that level of consumption. Your tank might consume a lot less, but I wouldn't count on it.

Sps Dream

New member
I'm sure It's harder %20 water change than set up calcium ractor. If sometimes you can't change enoug water you'll risk all system. Think again.