View Full Version : Ca/kH Consumption Question

06/24/2017, 02:57 PM
I've been in the hobby for a long time but I've got a question I haven't seen asked before. I set up a new 125 about four months ago and knock on wood, everything is doing really well. It's an SPS dominated tank with about twenty small to medium sized frags of a variety of SPS and a few LPS. All frags are growing rapidly and encrusting well with good color.

I use Reef Crystals which, on my salifert kits, mix at about 8.4 kH and 485 Ca. So, my question is that despite seeing fast growth of my corals, my regular tests don't show any consumption of either kH or Ca. I do 15% water changes about every two weeks. I see a very slight bump up after the water change so I guess there's a bit of consumption but it's barely noticeable.

So, my question is how much Ca and kH is consumed by a give mass of coral (pretty much any SPS).

06/24/2017, 05:13 PM
first off, iorc should be mixing up much higher in alkalinity (11-12 ish).

second....you pretty much answered your own question about alk/ca consumption....It's my opinion that coralline algae uses much more alk/ca then most people would think. I have a lot of rocks covered with coralline and also the back glass. I have taken out large colonies of sps with no/very little change in dosing.

06/24/2017, 05:18 PM
I guess yr sps is small colony or frags? If its a large colony then its a good thing! Peace of mind 😁 because its consuming very little component

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06/25/2017, 01:51 PM
first off, iorc should be mixing up much higher in alkalinity (11-12 ish).

Was just going to say this same thing.

I switched back to regular old IO because of the high alk, but I'm finding IO to be in the 9 to 10 range to(prefer to be at 8.0 to 8.5).

06/25/2017, 05:56 PM
I've got to try the calibration fluid that came with my Salifert kit. At least the level is consistent even if it's off on the low side.

06/25/2017, 06:24 PM
Interesting. I just tested the kit against the calibration fluid. The fluid states that it's at 6.7 kH. It tested at 7.7 kH. So, basically, rather than running at 8.4 (assuming it's a one to one relationship as opposed to some other scale) I'm really running at 9.4 kH. I'm not concerned about either number as long as it's consistent.

I also thought that RC runs at higher kH but, at least for the last two buckets, it's been very consistent at this level.

06/26/2017, 04:46 AM
What answer are you expecting here?
for every 1oz of corals consumes X alk and Y cal?

Don't think thats possible..

And you might want to get a second source to run a test for you..
RC should be/is higher..

06/26/2017, 04:54 PM
I think I've got a red sea kit somewhere so I'll retest. As I mentioned, I'm not particularly concerned about the number so long as it's very stable. I grow chaeto like crazy so my system is not ULNS and somewhat elevated kH doesn't really concern me. That said, I'll be switching to IO when I run out of the RC.

Yea, I know a specific ratio of consumption isn't possible. I was just curious as to why I wasn't seeing greater consumption considering the coral growth rates. That said, I don't have much coraline algae yet so it may be just taking it's time.

06/27/2017, 04:31 AM
Yep.. lack of coralline algae and being that they are only "frags" in a decent amount of water you just aren't seeing the consumption rates one would normally have with a more mature tank with larger colonies,etc...

06/27/2017, 11:04 AM
What is the sg? Obviously the salt mix kh will be lowere if the sg is less than 1.026.

Consumption is generally 20ppm calcium to 50ppm (2,8dkh) alk. Coraline, some bacterial activity , zooxanthelae contributions to the HCO3 mix , variety in sps species ,pH and a host of other things make consumption a tank specific measure not generalizable to sps corals in a reef tank as a category.IMO.