Using Alk but not Ca?

[thabizness]

I have started dosing Alk in my tank hourly using a 1.1ml dosing pump for 21 seconds a hour. This keeps me at 8.512 dKh.

My Ca tests about 420-440 daily without having to dose. Is that weird to use so Alk but no Ca?

[disc1]

Maybe your water changes are keeping up with the calcium but not the alk.

How long has this trend been going on? For every 1dkH of alk that you use, you should only drop 7ppm of calcium. That's not enough to see on your test and often leads to the illusion that calcium isn't being used when in fact it really is.

[thabizness]

Trend for about a month. Water change bi weekly.

[tmz]

For each dkh of alk (50ppm) used in calciumn carbonate precipitation only about 20ppm of calcium are used .So, water changes may be making it up or any calcium drop may be at a level small enough to be missed in the test.

[brad_G]

Wait! Disc said 1 dkh is 7 ppm TMZ says 1 dkh is 20???? Not criticizing but someone has got to be wrong. I was thinking the ratio was 1 meg/l to 17-20 ppm can depending on species and magnesium and phosphate intake.

[tmz]

Ooops ;I meant to say for each 2.8 dkh/1meq/l /50 ppm to approximately 20ppm calcium.

[nicholasb]

I would start dosing both.

[thabizness]

What would be the starting dose if I'm not seeing a drop?

[bertoni]

The typical two-part can be dosed in equal volumes. I'd start there and see how it goes.

[ItzJustinN]

my advice, dont fix it if its not broken.

my reef has been doing the same thing (using KH but not CA)
atleast not using enough to where i need to dose CA.

i would just keep testing CA to make sure it stays within params
and only dose if needed.

[ViktorVaughn]

I have the same thing going on in my tank now for 2+ months now. Calcium always stays between 420-450 ppm with bi-weekly water changes but in order to keep my alkalinity at 8.5 I need to dose daily, I have some pretty decent sized SPS colonies too so not really sure why I am not using more calcium. I've tried finding some explanation to this as it seems that calcium and alkalinity should both be getting used not just alk.

[thabizness]

glad too see im not the only one.

[Randy Holmes-Farley]

It is using both, and likely close to equally, as there really isn't much other way for alk to rapidly decline, but the calcium is boosted in many tanks by the artificially high calcium present in many salt mixes.

It also takes a long time to see the calcium drop against the high levels and the test kit noise. :)

[wayne in norway]

Unless of course you have a heavily stocked or messy tank, in which case alk will be used buffering wastes.

[Randy Holmes-Farley]

Well, only if nitrate is being produced excessively and is removed by water changes (which itself probably messes with demand more than the nitrate production since few salt mixes exactly match any specific reef tank calcium and alkalinity).

I think that all other "waste" effects will not reduce alkalinity anywhere near as much as calcification.

I discuss such issues in detail here:

When Do Calcium and Alkalinity Demand Not Exactly Balance?
http://reefkeeping.com/issues/2004-12/rhf/index.htm

[Jone]

taggin

[thabizness]

Thanks for that link. Good reading. I think my biggest problem is that my Ca testing was off and unreliable.

Since I started this post I got a Salifert test kit for Ca. I have slowly been replacing my API test kits with either Hanna or Salifert because I have been doubting the reliability of API.

The Salifert test does register a drop in Ca over a weeks time which is what I have used to set the doser.

We will see in the coming weeks tho.

[Randy Holmes-Farley]

:thumbsup:

Good luck. :)