ALK consumption

I've calculated my ALK consumption and it is 0.3 meq/L (0.84 DKH) per day.

On ther other hand, mag and CAL have virtually zero consumption.

I am dosing a lil CAL only once every 2..3 weeks and replenishing mag with new salt during water changes.

So that basicaly means I have to and been adding 3 caps of Seachem Reef Carbonate every evening to maintain my water at 8.5 DKH.

Is this level of consumption normal? Seems like a lot and strange that it's only ALK that drops.

My params are:
Sal: 1.025
Temp: 79
CAL: 420
Mag: 1430
ALK: 8.5 (drops by 0.84 every day)
NH3/NO2/NO3 = 0/0/5

Thanks.

 

There really is no "normal" for a reef. Every tank is completely different, and depending on your exact coral stocking, some levels will drop more than others. It looks like you're shooting for good parameters, and as long as everything looks good and shows good growth, I would keep up the same.

 

Magnesium consumption by corals is pretty nominal. There is slightly more consumption by coralline algae. Also, there can be abiotic precipitation with calcium carbonate as this is precipitated, or if a fresh new source, such as new dry sand or dry rock is added. It is common to have to mg drop in a new tank for example, but tends to be much less so once the tank is established. However, in a typical, established tank, it would take days, if not weeks to really get enough of a drop to detect.

Ca consumption is roughly proportional to alk consumption. And is about 7.14ppm ca per 1 dkh alk (or ~20ppm per 1 meq/L Alk). So, if your at 8dkh and 400ppm ca, and drop 1dkh per day, after a day you'd be at 7dkh, but approx. 393ppm ca, and ca test kits aren't accurate enough to detect this change, so, it would seem as if it hadn't dropped, even for a number of days.

So, it's not that ca and mg aren't dropping, they are just expected to drop at a rate which is virtually undetectable compared to alk.

Also, FWIW, .84 dkh per day drop is pretty small in the big scheme of things, I see around twice that and 3 or 4 times that isn't really uncommon in some tanks, especially if there is a lot of hard corals and coralline algae.

 

Thanks guys. Did not realize ALK/CAL consumpton was tied together like that. Is that formula exact or an aproximatin that can vary?

I guess it's time to get a dosing pump and setup ALK on auto-drip.

 

It is an approximation. I dose 30ppm per day of calcium and almost 2meq/l of alk per day. As Mikerice stated you will need to see what your tank uses. This will also vary over time as your corals grow.

 

Give this a read. Made a lot of sense.

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com

 

There is a stoichiometric ratio between ca and carbonate. Alk is only a surrogate measure for bicarbonate however, as this is what we are interested in, but are unable to test for directly.


Here, in addition to the article provided by kss2801, this should also be more than you probably want to know about ca and alkalinity
Calcium and Alkalinity by Randy Holmes-Farley - Reefkeeping.com