Should we test Calcium?

[BradB]

Everyone with hard corals tests Calcium, I've been for years, but am starting to think it is a waste of time and money. I add Calcium and Alkalinity in balanced parts, test Alkalinity, and a small variation in Alkalinity can be a big deal. I've seen no difference between 350ppm and 420ppm Calcium. On the very rare occasion Alkalinity is fine and Calcium is high or low, I find myself assuming it is probably a problem with my test kit and not my water. So what advantage does testing Calcium have?

 

[nova65ss]

Only time I test calcium is if my alk gets off. Otherwise it's about once a month maybe.

 

[Potatohead]

It seems reasonable to check it - Getting complacent is when things to bad. If you want to check the tank less I would definitely check any new boxes/buckets of salt to make sure they are in-line. Otherwise once every 2-4 weeks is probably ok.

 

[Randy Holmes-Farley Verified Community Expert]

It is prudent to keep track of it, but I didn't measure it for many years because I knew that between the water changes with normal IO and dosing of limewater, it would be maintained OK.

 

[PatW]

Testing for calcium does feel like a waste of time if you it in conjunction with ALK dosing.

I test every week ..... or two just for form’s sake. I figure that is cheap insurance.

 

[3mm3]

I say that if you are dosing calcium as with 2 part then test on a routine.
With Kalk or calcium reactor I literally test twice a year. Only exception to that is if I have odd test results on ALK and Magnesium.

 

[BradB]

Something (Calcium or anything else) is only worth testing if the result of the test influences further action.

If I am using Instant Ocean and adding balanced Ca and Alkalinity, how high or low should I let Calcium get before I take action? I am using Instant Ocean, so any water changes are going to push me back towards 400ppm and 11 dKH. If I am dosing correctly, Alkalinity should be stable at 11dKH and Ca should be balanced. So if I measured 350ppm Ca and 11dKH, or 420ppm Ca and 11dKH, I will slowly drift back to 400ppm and 11dKH. I haven't noticed much difference between those numbers, and Acropora does better with stability than perfection, so what is wrong with slowly drifting back?

 

[d2mini]

Running a Calcium Reactor, I pretty much know that Calcium will be where it needs to be if my Alk is good.
But I will check it occasionally just out of curiosity.

 

[Randy Holmes-Farley Verified Community Expert]

Something (Calcium or anything else) is only worth testing if the result of the test influences further action.

If I am using Instant Ocean and adding balanced Ca and Alkalinity, how high or low should I let Calcium get before I take action? I am using Instant Ocean, so any water changes are going to push me back towards 400ppm and 11 dKH. If I am dosing correctly, Alkalinity should be stable at 11dKH and Ca should be balanced. So if I measured 350ppm Ca and 11dKH, or 420ppm Ca and 11dKH, I will slowly drift back to 400ppm and 11dKH. I haven't noticed much difference between those numbers, and Acropora does better with stability than perfection, so what is wrong with slowly drifting back?

How much drift there is will depend on exactly what you are dosing, but you should anticiptate some drift in calcium while maintaining alkalinity.

With limewater/kalkwasser (as I dosed for 20 years), there is a constant and steady drift upwards in calcium if maintaining alkalinity with it. I used normal IO, but my calcium was 472 ppm last time I tested it via Triton.

With a two part or balling, etc, the change in calcium over time, while maintaining alkalinity, will depend both on how well the design of the two part matches the exact ratio of calcium to alk demand in your tank, which involves things like how much magnesium and strontium are being taken up, as well as how the two part is designed. it also depends, of course, on how much of each you dose. With manual dosing, it might be randomly up or down each time for each part, so perhaps averaging out, but with dosing pumps, slight differences in the doses delivered will add up over time.

There are also a few ways that alk demand does not exactly match calcium demand (especially rising or falling nitrate levels, and the use of sulfur denitrators).

So I think it is worth monitoring, but perhaps substantially less often than alkalinity.

 

[BradB]

It can and does drift up and down in my tank, but again, I don't see this affecting anything other than my test results.

I am surprised you can hit 472ppm Ca without a major precipitation problem unless your alkalinity is too low. 15 years and I've never seen mine above 450ppm. But this proves my point - the Calcium level doesn't matter.

 

[Randy Holmes-Farley Verified Community Expert]

It can and does drift up and down in my tank, but again, I don't see this affecting anything other than my test results.

I am surprised you can hit 472ppm Ca without a major precipitation problem unless your alkalinity is too low. 15 years and I've never seen mine above 450ppm. But this proves my point - the Calcium level doesn't matter.

I don't think it proves the point entirely. If the calcium drifted down into the 300's, it may become limiting to coral growth.

Fortunately, there's nothing wrong with calcium as high as 500 or 550 ppm (some salt mixes start that high). High calcium is less of a concern than low calcium.

A boost in calcium from 400 to 550 ppm is about the same in terms of precipitation likelihood (e.g., calcium carbonate supersaturation) as an alk boost from 7 to 9.6 dKH or a pH rise from 8.2 to 8.34 (pH is a massive driver of precipitation as bicarbonate shifts to carbonate).

 

[chipmunkofdoom2]

So what advantage does testing Calcium have?

A Salifert calcium test kit will get you about 50 tests and costs $18. That's about $0.35 per test. I can test Ca, Alk and Mg in under 10 minutes, so for the purpose of our discussion here, let's say it takes you about 5 minutes to test calcium. Assuming you test once a week, which is likely enough for most reef tanks, testing calcium only "costs" you $0.35 and 5 minutes per week.

I fail to see a disadvantage to testing calcium when the cost is only slightly more than a quarter and uses just 5 minutes of your time.

 

[BradB]

A Salifert calcium test kit will get you about 50 tests and costs $18. That's about $0.35 per test. I can test Ca, Alk and Mg in under 10 minutes, so for the purpose of our discussion here, let's say it takes you about 5 minutes to test calcium. Assuming you test once a week, which is likely enough for most reef tanks, testing calcium only "costs" you $0.35 and 5 minutes per week.

I fail to see a disadvantage to testing calcium when the cost is only slightly more than a quarter and uses just 5 minutes of your time.

A extra skimmer cleaning or powerehead cleaning takes the same 5 minutes and benefits my tank. If the kit expires in 2 years, it is $9 per year, not $0.35 per test, unless you test twice a month. Still not a lot, but more than $0.35.

 

[chipmunkofdoom2]

A extra skimmer cleaning or powerehead cleaning takes the same 5 minutes and benefits my tank. If the kit expires in 2 years, it is $9 per year, not $0.35 per test, unless you test twice a month. Still not a lot, but more than $0.35.

My original point was that 5 minutes a week to test and $18 a year for test kits is not that much. Many people pay twice that to simply ship livestock to them. Single coral frags retail for hundreds, sometimes thousands of dollars. If you haven't spent over a thousand dollars setting up your reef, you've either been very smart with your purchasing or have a very bare-bones tank. When you consider all the money and time we spend on this hobby, it just sounds silly to say that $20 a year for a test kit and 5 minutes a week to test is "too much."

If you don't want to test your calcium levels, that's fine. I won't try to convince you any longer. I just can't understand why so many people in this hobby are so averse to testing their water. It's not that difficult, it doesn't take up that much time, and it's not that expensive.