Odd Test Results

Ok, so I got some new Salifert kits to replace the Red Sea ones I had before. The RS calcium was easy enough, but it was measured in increments of 50ppm, so I wanted something a bit more accurate. The alk was garbage.

I tested the first night, got 8 dkh for alk, and 450 ppm calcium. I dosed alk, according to BRS's calculator, up to a desired result of 10 dkh.

I tested 3 days later, and got results of 10.2dkh alk, and 420ppm calcium. I figured the alk was higher as a result of a low number for tank gallonage. So, I again dosed according to BRS's calculator, so that calcium would be up to 450ppm, using the same number of gallons.

I then tested again tonight (3 more days), and got a result of 450ppm calcium, and 8.3 dkh. Is it just me, or are these numbers outright weird? I can't imagine my gallonage estimate being off by such an amount as to cause this discrepancy. It seems the tank's inhabitants are using a bunch of alk, then a bunch of calcium, and alternating like that.

I say that I can't imagine my gallonage being off by this much, because in order to have 480 ppm calcium after dosing it, I would need to be that far off. It would need to be 480 ppm calcium, otherwise I wouldn't be getting a result of 450 3 days after dosing, while knowing my consumption is about 10 ppm per day from the first gap.

 

They dont seem weird to me

its the 20 - 1 ratio almost

when you increased ALK by 2 - your calc dropped 30
you increase Calk by 30 and your Alk drops by 2

whats your Mag level - is it able to support your 2 target numbers?

Steve

 

Interesting

Do you have values for your pH or mag ?

If you mag value is low you may want to consider that as the cause for the fluctuating alk.

 

My mag is about 1300. Is that too low to support my alk/cal values?

 

this doesnt seem out of place to me... seems about right.
as alk is increased, ca decreases. the only way to make them both be high is to have a higher magnesium level. as you dose ca, your alk will always decrease, and as you dose alk, your ca will always decrease.

trick i have found for keeping the ca stable (and then the alk will follow) is to shoot to have your mg at a very stable, non-fluctuating level roughly 3.1-3.5 times the level of your ca. this should cause everything to fall into place nicely. Then after a few days your ca will level out, and a few days later your alk will then follow.

once your there, by monitoring alk closely you can then know if anything is going to change; a fluctuation in alk will mean a fluctuation in ca is to follow in a few days, and possibly a fluctuation in mg after that if its significant enough.

 

from your first post I assume your shooting for ca 450ppm?
if thats the case then i would take mg up to 1395ppm and see if things level off then

 

Yeah, I was aiming for 450 calcium and 10 dkh.

For future reference, what's the formula for the maximum alk/cal combo?

 

Dingo said it all
but yes 1300 does seem low to support those numbers
I maintained 440 Calc and 9 DKH with a Mag level between 1410 and 1450

Steve

 

IME, alk is usually variable based on things like: type of dosing, oxygen in tank, ca reactor, kalk.

But the [Mg] determines what the [Ca] is... Ca is usually (1/3.1) times Mg or put in easier terms, Ca x 3.1 = Mg.
everything else is just equilibrium
Im sure you already know about it but re-read randy holmes-farley's article in reefkeeping magazine again Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com

 

I aim for dKH of 10-11, Calcium of 440-460 ppm and Magnesium of 1400-1450 ppm. I think your Magnesium is too low and you are chasing Calcium and Alkalinity. Adjust Mag first and no more than 100 ppm per day. I like a lesser rate increase so I shoot for 50 ppm per day. Then you can go after Alkalinity and Calcium.