View Full Version : Do I have to test both? Ca Alk

06/16/2014, 11:35 PM
Do I need to test for calcium and alkalinity? If you have one value doesn't that give you the other because of the chemical balance?

The last tank of the month guy only tested for alk and I'd much rather do that then test for both.

06/17/2014, 02:01 AM
You could do that, when you're sure you're dosing in balance.
However, you still need to check calcium every now and then, just to confirm you're still on track.

I have combined the "postponed" tests and do calcium, alk, magnesium, strontium, potassium and iodine once a week.
And as I am getting more and more confident with the results, I sometimes even skip a week.


Randy Holmes-Farley
06/17/2014, 05:06 AM
Depending on how you dose calcium and alkalinity, measuring alk and adjusting the dose to that and then only once in a while measuring calcium is a fine plan. Do not do it the other way around, for several reasons. That way doesn't work out.

To do this, you need to sue a balanced calcium and alkalinity method, such as a two part, limewater (kalkwasser) or a CaCO3/CO2 reactor. ;)

06/17/2014, 08:14 AM
I test Alk once or twice weekly (easy test to do), and test Ca every few weeks (if even that). If I'm trending one way or the other on Alk I will make a small adjustment to how much kalkwasser I add throughout the day.

If I think I have a balance problem with my Alk/Ca balance, I do several Ca tests with separate kits and try to see how far I might be off. I rarely end up making "balance adjustments".

On Mg it's much the same...I test every once in awhile, and make an addition if necessary. Thankfully Mg can have a fairly large range in our systems...so "about" is often "good enough" with Mg.

06/17/2014, 04:16 PM
I ended up testing calcium every few months, at most, but I always tested alkalinity every 2-3 weeks, more often every week. As long as you're using one of the suggested balanced additives, you probably won't need to test both all the time.

06/19/2014, 01:03 AM
I usually dose 2 part in equal amounts, but lately I have been using kalkwasser. So if I follow Randy's advice I should be good testing alk and the occasional calcium test. I'd also like to know how I can get my calcium value after testing alk? Is there an equation that will convert your alk value to the associated calcium value?

On another note, What is a good alk kit? I like salifert, but i want to try lamotte if the result are just as accurate. The lamotte kit seems easier to use and the equipment seems to be of better quality. Don't get me wrong the salifert test is quick and easy but I'm looking for even easier and testing equipment that doesnt fade after multiple uses. BTW I hate the hanna checker, but I have the phosphate test kit cause I've reaf that the readings are almost dead on.

Randy Holmes-Farley
06/19/2014, 04:50 AM
You can't get a calcium value from an alk value.

What you can do is have confidence that if you only used kalkwasser and keep alkalinity reasonably the same, the calcium will be the same unless a water changes with a mix different than the tank changed it. :)

You can calculate the change in calcium if you know the change in alkalinity, and it went up or down in a balanced fashion: 18-20 ppm calcium for each 1 meq/l (2.8 dKH) of alkalinity. :)

06/20/2014, 02:21 AM
So if I test calcium and alkalinity one week, then only test alkalinity the next week and my Alk results are the same as the week before, I can be fairly confident that my calcium is the same as the week before.

Now lets say I test Ca and Alk and my values are 420ppm and 8.8dKH, respectively. The next week I test Alk and I get a value of 6.0 dKH, I can be fairly confident my calcium is at 400 ppm.

Now, with all that being said, I should probably test Ca every few weeks due to my 10% weekly water change, as I have no idea what the Ca and Alk values are of my mixed saltwater.

06/20/2014, 02:31 AM
AND.... If I test my mixed saltwater and find the Ca and Alk values I can set up a mixing equation(NewSaltWaterVol x Conc1 + (.9)TankVol x Conc2 = TankVolume x ConcT) to find my Ca and Alk Values of the display tank after I add new saltwater.

Or.......... I can quit being a cheapskate and test Ca and Alk and not have to worry about all this!!!!!!!!!!!!!!

06/20/2014, 02:36 AM
and............... I just hit 50 posts!! Now I can finally see what everyone is selling!!!

Randy Holmes-Farley
06/20/2014, 03:51 AM
Yes to all of that, except that a water change could mess up those assumption every time you do one, and might do it rapidly since some salt mixes may depart from tank values considerably. :)

06/21/2014, 12:11 AM
Do you recommend any Alk and Ca tests kits?

Randy Holmes-Farley
06/21/2014, 06:57 AM
It's been a while since I actually compared commercial kits. I used and liked the Salifert kits, but then switched to a DIY alk test. Now I rarely test either calcium or alkalinity since I know my husbandry methods are working fine. :)

06/21/2014, 07:07 AM
FWIW, most folks on the forum tend to use the Salifert kits. They're easy to use, accurate, and relatively inexpensive from a supplier like Bulk Reef Supply or Marine Depot.

06/21/2014, 07:27 PM
I like salifert too, but I want to try lamotte. Just wondering if it's as accurate as salifert. I read somewhere that salifert was within 12% of real results, if lamotte can replicate this accuracy I would switch over.

06/22/2014, 07:17 AM
LaMotte used to have the reputation of being the pinnacle of portable environmental water test kits. Not sure if that's still true, but they definitely make some good products. They tend to be quite a bit more expensive than the test kits marketed to hobbyists, however.

06/22/2014, 02:37 PM
LaMotte alkalinity kits should be okay, although they're calibrated for fresh water, and will read a little low for saltwater. People have had good results with them, although it's been a bit since I read a review.