What is the ideal alkalinity

[BryanB]

I have kept my tank at 10.4 or so because I was understanding it would be rapid growth ( Red Sea rapid growth calls for 12.?) I had a conversation yesterday at reefapalooza that made me think dropping it to about 7.8-8.2. What are your thoughts?

 

[huuta]

I always tried to keep it steady at 9.Key word is steady.

 

[BryanB]

Stability isn't a problem i am running a Ca reactor

 

[deerhunter06]

imo this is a loaded question. There are other variables that make higher Alk ok vs lower alk. Like phos and nitrates if you are running ULN and you have higher alk IME you will burn the tips of your SPS. NSW alk is 7

 

[glb]

It depends on your other news numbers, such as salinity, mg and ca. I think temp matters too. They all need to be in balance with one another. Randy Holmes Farley has some great articles in the stickies section of the Reef Chemistry forum. If you have an Alk of 10 for example, that would correspond to certain numbers for ca and mg. So if the proportions aren't right, things get out of whack. I'm trying to keep my Alk at 10kh because it's in the middle of the range so I have some wiggle room. But the ca and mg numbers need to correspond. I think there are some reef calculators online where you put in your Alk and it will tell you what your ca and mg levels should be for that Alk.

 

[Randy Holmes-Farley]

There is no ideal alkalinity that fits all aquaria and all aquarist goals. Higher alk can give faster growth in hard corals, but can be a problem in ULNS SPS systems.

i discuss it here:

https://www.reef2reef.com/forums/re...-coral-reef-aquarium-randy-holmes-farley.html

from it:

Alkalinity


Like calcium, many corals also use "alkalinity" to form their skeletons, which are composed primarily of calcium carbonate. It is generally believed that corals take up bicarbonate, convert it into carbonate, and then use that carbonate to form calcium carbonate skeletons. That conversion process is shown as:


HCO3- → CO3-- + H+


Bicarbonate → Carbonate + proton (which is released from the coral)


To ensure that corals have an adequate supply of bicarbonate for calcification, aquarists could just measure bicarbonate directly. Designing a test kit for bicarbonate, however, is somewhat more complicated than for alkalinity. Consequently, the use of alkalinity as a surrogate measure for bicarbonate is deeply entrenched in the reef aquarium hobby.


So, what is alkalinity? Alkalinity in a marine aquarium is simply a measure of the amount of acid (H+) required to reduce the pH to about 4.5, where all bicarbonate is converted into carbonic acid as follows:


HCO3- + H+ → H2CO3


The amount of acid needed is equal to the amount of bicarbonate present, so when performing an alkalinity titration with a test kit, you are “counting” the number of bicarbonate ions present. It is not, however, quite that simple since some other ions also take up acid during the titration. Both borate and carbonate also contribute to the measurement of alkalinity, but the bicarbonate dominates these other ions since they are generally lower in concentration than bicarbonate. So knowing the total alkalinity is akin to, but not exactly the same as, knowing how much bicarbonate is available to corals. In any case, total alkalinity is the standard that aquarists use for this purpose.


Unlike the calcium concentration, it is widely believed that certain organisms calcify more quickly at alkalinity levels higher than those in normal seawater. This result has also been demonstrated in the scientific literature, which has shown that adding bicarbonate to seawater increases the rate of calcification in some corals. Uptake of bicarbonate can consequently become rate limiting in many corals. This may be partly due to the fact that the external bicarbonate concentration is not large to begin with (relative to, for example, the calcium concentration, which is effectively about 5 times higher).


For these reasons, alkalinity maintenance is a critical aspect of coral reef aquarium husbandry. In the absence of supplementation, alkalinity will rapidly drop as corals use up much of what is present in seawater. Water changes are not usually sufficient to maintain alkalinity unless there is very little calcification taking place. Most reef aquarists try to maintain alkalinity at levels at or slightly above those of normal seawater, although exactly what levels different aquarists target depends a bit on the goals of their aquaria.


Interestingly, because some corals may calcify faster at higher alkalinity levels, and because the abiotic (nonbiological) precipitation of calcium carbonate on heaters and pumps also rises as alkalinity rises, the demand for alkalinity (and calcium) rises as the alkalinity rises. So an aquarist generally must dose more calcium and alkalinity EVERY DAY to maintain a higher alkalinity (say, 11 dKH) than to maintain 7 dKH. It is not just a one-time boost that is needed to make up that difference. In fact, calcification gets so slow as the alkalinity drops below 6 dKH that reef aquaria rarely get much below that point, even with no dosing: natural calcification has nearly stopped at that level.


In general, I suggest that aquarists maintain alkalinity between about 7-11 dKH (2.5 and 4 meq/L; 125-200 ppm CaCO3 equivalents). Many aquarists growing SPS corals and using Ultra Low Nutrient Systems (ULNS) have found that the corals suffer from “burnt tips” if the alkalinity is too high or changes too much. It is not at all clear why this is the case, but such aquaria are better served by alkalinity in the 7-8 dKH range.
As mentioned above, alkalinity levels above those in natural seawater increase the abiotic precipitation of calcium carbonate on warm objects such as heaters and pump impellers, or sometimes even in sand beds. This precipitation not only wastes calcium and alkalinity that aquarists are carefully adding, but it also increases equipment maintenance requirements and can “damage” a sand bed, hardening it into a chunk of limestone. When elevated alkalinity is driving this precipitation, it can also depress the calcium level. An excessively high alkalinity level can therefore create undesirable consequences.


I suggest that aquarists use a balanced calcium and alkalinity additive system of some sort for routine maintenance. The most popular of these balanced methods include limewater (kalkwasser), calcium carbonate/carbon dioxide reactors, and the two-part/three part additive systems.


For rapid alkalinity corrections, aquarists can simply use baking soda (sodium bicarbonate) or washing soda (sodium carbonate; baked baking soda) to good effect. The latter raises pH as well as alkalinity while the former has a very small pH lowering effect. Mixtures can also be used, and are what many hobby chemical supply companies sell as “buffers”. Most often, sodium carbonate is preferred, however, since most tanks can be helped by a pH boost.

 

[scardall]

thanks for the data/advise

thanks for the advise here.

 

[StikHedRon]

I would say that NSW would be best! But I keep mine at 7.5-8 dkh

 

[Co0lReEFguY]

10 dkh? Isn't that to high I always heard 8.5 to 9 was good.

 

[KoleTang]

10 dkh? Isn't that to high I always heard 8.5 to 9 was good.

It's just about achieving the ideal balance of Phosphorus, Nitrogen, and Carbon.

 

[Randy Holmes-Farley]

10 dkh? Isn't that to high I always heard 8.5 to 9 was good.

Unless it is an Ultra Low Nutrient System, anywhere in the 7-11 dKH range is fine, and corals will likely grow faster at the higher end.

 

[Av8Bluewater]

My corals seem happier at 7-8. ULNS,Zeo tank.

 

[Big Larr]

Anything 8 - 9 dkh and my acros loose their color and brown out and everything stops growing try to keep mine at 8

 

[Big Larr]

Oops sorry meant anything over 9dkh

 

[Randy Holmes-Farley]

Oops sorry meant anything over 9dkh

That is generally only in a low nutrient tank. It isn't true in other situations that corals stop growing as alkalinity rises. In fact, they are known to grow faster in higher alkalinity.

 

[Big Larr]

Oh cool guess I need dirtier water then but my nitrates always test at zero

 

[revhtree]

I'm trying to keep mine around the 9-10 DKH range for now.

 

[van7271]

I try to keep mine between 9 to 10.

 

[rock_lobster]

A stable one. That is between 7-10

 

[Fercho]

In my experience, SPS polyp estension is greater (i would even say crazy polyp ex) with Alk level between 7-8.
Alk above 8 and polyps dont extend so much.
But my usual Alk range fluctuates between 7-7.8
My No3 i keep between 3-6
When my parameters are stable, my corals start growing fairly quickly.
But as we all know, some corals grow faster and some slower.