Salinity, Alk, and CA

PeaBrain · May 28, 2020

I would like some feedback on what I have come to understand about these three, and optimum levels of each in a reef aquarium.

I have been advised by a local coral farmer the following:

Keep salinity lower. 1.022-1.024. This allows Alk to remain on the higher end (10-12) which promotes faster coral growth. Having Alk higher also gives the hobbyist a time buffer if Alk slowly drops. Higher Alk will also lower CA, but having higher sustainable Alk levels is more important.

Do this jive with anyone?

Auquanut · May 28, 2020

Following.

madweazl · May 28, 2020

My thoughts are that everything in the ocean has evolved to live within its natural parameters. That means an Sg roughly 1.026, dKh around 6.8, and calcium levels around 390 so I tend to keep my aquarium closer to those levels. There is a fairly wide margin where everything grows so absolutes are unnecessary.

Larry L · May 28, 2020

I think the answer partly depends on what you are trying to do in your tank. Obviously for a coral farmer a primary goal is fast growth, but in my tank which is relatively well filled in now, faster growth just means more maintenance pruning for me, and I'd rather focus on coral health and stability and color.

Randy Holmes-Farley · May 28, 2020

PeaBrain said:
I would like some feedback on what I have come to understand about these three, and optimum levels of each in a reef aquarium.

I have been advised by a local coral farmer the following:

Keep salinity lower. 1.022-1.024. This allows Alk to remain on the higher end (10-12) which promotes faster coral growth. Having Alk higher also gives the hobbyist a time buffer if Alk slowly drops. Higher Alk will also lower CA, but having higher sustainable Alk levels is more important.

Do this jive with anyone?

Not really. i do not think lower salinity allows higher alkalinity.

PeaBrain · May 29, 2020

Randy Holmes-Farley said:
Not really. i do not think lower salinity allows higher alkalinity.

Would a higher salinity promote higher Calcium tendencies?

Randy Holmes-Farley · May 30, 2020

PeaBrain said:
Would a higher salinity promote higher Calcium tendencies?

When you mix artificial seawater, the concentration of everything in it reflects the salinity.

Once mixed, and you are supplementing the tank, calcium is not particularly related to salinity except as it relates to calcium in the water changes (if any are performed).

PeaBrain · May 30, 2020

Randy Holmes-Farley said:
When you mix artificial seawater, the concentration of everything in it reflects the salinity.

Once mixed, and you are supplementing the tank, calcium is not particularly related to salinity except as it relates to calcium in the water changes (if any are performed).

So, no?

Randy Holmes-Farley · May 30, 2020

PeaBrain said:
So, no?

You asked a very vague question, and I tried to give an accurate answer:

"Would a higher salinity promote higher Calcium tendencies? "

what does "promote higher tendencies" mean?

So I answered as best I could. It can have many different answers at many levels of chemical understanding and chemical interpretations.

If I add sodium chloride to seawater, that will reduce the tendency to form calcium carboante precipitates by a very small amount. Too small to be noticeable in a reef tank, IMO.

If I raise salinity by adding magnesium sulfate, that has a bigger and possibly noticeable effect on the reduction in precipitation. If that means "promote higher Calcium tendencies" then it might be a tentative yes.

By the same notion, it also "promotes higher alkalinity tendency tendencies".

That was the basis of my negative response to your original suggestion that

"Keep salinity lower. 1.022-1.024. This allows Alk to remain on the higher end (10-12) "

I think the reverse is clearly true, although the effect is small. Higher salinity will allow higher alk (and calcium) to be maintained. In the extreme, the amount of alk and calcium that can co-exist in fresh water is very low.