Elevated Ca+ and TA levels

[mook1178]

Is the reason for elevated Ca and alkalinity in reef tanks just to grow the coral faster? To combat elevated CO2 levels in the home?
With the dosing apparatus these days alkalinity and Ca can stay relatively stable so I think the argument of reduction is moot.
Thoughts?

 

[Randy Holmes-Farley]

Calcium is not generally believed to be growth limiting and I don’t think the values matter in the 400-550 ppm range,

Many hard corals do calcify faster at higher alkalinity and hence grow faster. The carbonate/bicarbonate is the limiting factor there.

 

[mook1178]

So it really is just for faster growth rates?
No other major reason?

 

[Randy Holmes-Farley]

Mostly, yes.

It also haps bring up pH and/or reduce possible skeletal dissolution at very low pH, which is also a setting where growth may slow greatly.

I've seen few other claimed reasons for wanting higher alkalinity than about 7 dKH.

 

[mook1178]

Mostly, yes.

It also haps bring up pH and/or reduce possible skeletal dissolution at very low pH, which is also a setting where growth may slow greatly.

I've seen few other claimed reasons for wanting higher alkalinity than about 7 dKH.

Yeah that was my thought of combating high CO2 levels. I may run some sims in CO2sys to see where I want to run my TA at with the average CO2 levels in the room I am setting up in. Then I can see where my pH will land.

 

[mook1178]

Well and approximate pH at least. Once I see where phosphate levels land in my tank I can throw that in the equation as well.

 

[Randy Holmes-Farley]

The molecular basis of the effect of pH and alkalinity on calcification is somewhat complex.

Calcification ultimately needs carbonate. But what exactly is the source? It's actually pretty hard to experimentally distinguish bicarbonate from carbonate as the ion taken up. I've never seen a paper actually try, despite throwing out statements that seem to implicate one or the other.

Is calcification faster at higher pH due to the ease of excreting the excess proton taken up if bicarbonate is the ultimate source of carbonate?

Or is the higher concentration of carbonate at higher pH the reason calcification is faster at higher pH?

I discuss this a bit here:

Alkalinity stability? pH stability? Are they even different?

It is currently the dogma of the reef aquarium hobby to say that alkalinity stability is very important for SPS corals, and that pH is not. Often, the very idea of someone trying to optimize pH is called “chasing numbers” as if that statement by itself shows it to be foolish. Since I have...

www.reef2reef.com

 

[mook1178]

I agree wholly with that statement.

I am not trying to speed the calcification process, I just want to make sure I stay in the 8.1 pH range to be as natural as possible to be able to use the ambient air and not run a line outside or in the attic.

 

[rtparty]

I have heard it said many times over the years with zero real world experience or evidence that higher alkalinity grows corals faster. Higher pH will certainly speed up growth but my growth "looks the same" whether I run 7 or 9dkh.

My tank is running right around 7.5-8dkh currently and growth is a major pest actually. So, if the theory is true, I don't see any upside to running higher alkalinity. Ambient CO2 is almost always the prohibitor in keeping pH up

 

[Randy Holmes-Farley]

My tank is running right around 7.5-8dkh currently and growth is a major pest actually. So, if the theory is true, I don't see any upside to running higher alkalinity.

Certainly a reasonable thought. Only newer tanks with few and smaller corals or coral farmers/resellers would seem to want or need the highest possible growth rate.