Minimum Alk Usage for Calcium Reactor

Husker · Aug 18, 2017

I have a 150 gallon SPS tank plumbed into a 55 gallon refugium and 75 gallon sump. Total water volume is about 160 gallons based on pre/post dosing of alk calculations.

The tank is new, but I now have close to 60 SPS frags that have been in my tank for a few days up to a month. Because of the slow growth and large water volume, I am only using about .3 dKH every 2 days. I am currently manually dosing, but I have a jebao doser and a My Reef Creations CR-2 Calcium Reactor with the Carbon Doser Regulator.

I have never used a calcium reactor due to having lower demand in previous tanks and am a serious novice when it comes to this piece of equipment (but not really reef tanks, in general). Here is my question: at what daily alk usage should I start using my calcium reactor (meaning, what is the minimum the calcium reactor can safely add without overdosing)? Would you recommend manually dosing 2 part until usage is high enough, or does the CaRx have a high enough minimal dose that I will need to set up the automatic dosing for a while first?

Randy Holmes-Farley · Aug 18, 2017

Reactors can be scaled as small as you want but they are inefficient when used to deliver only a small amount of alkalinity and calcium relative to their potential.

I'd generally use a two part and or limewater for most systems unless the tank is very large with high demand so cost becomes more of an issue.

Husker · Aug 19, 2017

Thanks for the reply! Do you mean inefficient in terms of using up the CaRX media? I already have all the components of the calcium reactor. I anticipated it eventually being the most efficient method of alk/calcium delivery for a SPS dominant system with water volume of about 160 gallons. This evaluation was partly based on your write ups. My understanding was that the lack of efficiency of a calcium reactor for smaller systems was due to the equipment costs. Is this correct?

I will say that 2 part dosing on this system could get expensive fast, as I am adding 34mL of each to replenish a 0.3 dKH drop. The usage should grow exponentially as all the frags settle in, so I just want to be as prepared as possible. Are you saying I could safely scale my calcium reactor setup to, say, 0.3dKH per day and gradually increase as the demand increases? Or would it be best to do limewater dosing until consumption is >0.5-1.0 dKH per today?

Randy Holmes-Farley · Aug 19, 2017

No, I mean inefficient in using CO2, unless it is a recirculating type with low flow out of it.

Do you have a reactor yet?

With your size system it is a better bet than a small system, and if you plan heavy SPS it is a good way to go.

Husker · Aug 19, 2017

Yes. I have a MRC CR-2 and I have the Carbon Doser regulator. I got the reactor in a trade with a local. It is an older calcium reactor with dual chamber. It is this one: http://www.myreefcreations.com/product-lines/calcium-reactors/standard-reactors/cr-2-dual.html

It seems like a pretty good one, but I haven't seen many people who use it so I don't know much about it.

Randy Holmes-Farley · Aug 19, 2017

If you already have it, I'd try it, and it will become more useful later.

The reason nonrecirculating (single pass)reactors are inefficient with respect to CO2 usage, and hence may lower pH more than "necessary" is that a certain amount of CO2 is needed to lower the pH before much dissolution of the media begins.

Thus for a tiny amount of added alkalinity and calcium, you still need a substantial amount of CO2.

Husker · Aug 19, 2017

Okay, thanks. That is just what I was wanting to know.

In that case, I will probably dose manually or use my doser for limewater until the alk demand raises a bit. I was planning on doing limewater dosing alongside the calcium reactor anyway to maintain pH, so I'll just start that off slowly. Thanks for the info.