Alk level, Does it matter?

[spud_53]

Just as the title states, what does everybody run their alk level at and what are the benefits/drawbacks of different levels

 

[Kershaw]

Anything between 7 and 12 I am happy with. Each tank I have had has naturaly chooses what it likes. Then I keep it there. My tank now I shoot for 8. I don't really know the bennifits of the differences in that range.

 

[spud_53]

That's kinda what I thought but most all people have different levels with the same success

 

[Catchemall]

Ok so I was discussing and learning some of this the other day with another member. Apperantley the higher the alk the higher you need to maintain nutrients and vice versa the lower the alk the lower your nutrients should be kept.

 

[spud_53]

Hmm never heard that before but maybe on my new system I'll try a lower alk number cause I always seem to have low nutrient systems and always keep alk around 9ish

 

[Catchemall]

@twilliard can you help me explain this better.

 

[Kershaw]

I have heard that higher levels of alk and increase coral growth. Also if you carbon dose you need to maintain alk below 8 or your coral and get bleached tips

 

[donnievaz]

I have heard that higher levels of alk and increase coral growth.

Only if you have the nutrient levels to support it. If you raise the ALK in a system with 0 nitrates and phosphate your corals will lose color and in some cases bleach out. The accelerated growth process requires fuel, in this case nutrients. I'm currently learning all this the hard way...

 

[Randy Holmes-Farley]

Higher alk leads to faster growth of many hard corals.

If nutrients are very low, one can get burnt tips from higher alk, which may be due to the growth outstripping available nutrients to grow the organic tissue fast enough to match the skeletal growth.

Lower nutrients can lead to lower zooxanthellae levels and that can lead to apparent better color since the zoox are golden brown, and so it is a balance between color and growth in many reef tanks.

 

[Randy Holmes-Farley]

Here's one of my standard blurbs on alk:

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 “buffersâ€. Most often, sodium carbonate is preferred, however, since most tanks can be helped by a pH boost.

 

[Catchemall]

Thanks @Randy Holmes-Farley that helps a lot! Makes me understand a lot about my tank now.

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)

 

[Frop]

My API reef test kit said my dKH was 12-13. Is that way too high? Is that an issue? I've been adding a pH up (pH @8.4) so maybe it's related?

 

[kennedpa]

I have heard that higher levels of alk and increase coral growth. Also if you carbon dose you need to maintain alk below 8 or your coral and get bleached tips

Where did you hear or read about this? I haven't heard this before and will be trying to drive a system with high nutrient addition and carbon dosing while keeping nitrate around 1 ppm.

 

[Catchemall]

I've heard it as well

 

[Randy Holmes-Farley]

It is established in the scientific literature that higher alk can lead to higher rates of calcification in corals:

for example:
http://onlinelibrary.wiley.com/doi/10.4319/lo.1999.44.3.0716/full

Bicarbonate addition promotes coral growth

Abstract
The addition of 2 mM bicarbonate to aquaria containing tropical ocean water and branches of Porites porites caused a doubling of the skeletal growth rate of the coral. Nitrate or ammonium addition (20 μM) to oligotrophic seawater caused a significant reduction in coral growth, but when seawater containing the extra bicarbonate was supplemented with combined nitrogen, no depression of the higher growth rate was evident. We infer that (1) the present dissolved inorganic carbon (DIC) content of the ocean limits coral growth, (2) this limitation is exacerbated by nitrate and ammonium, and (3) adding DIC increases coral calcification rates and confers protection against nutrient enrichment.

 

[donnievaz]

My API reef test kit said my dKH was 12-13. Is that way too high? Is that an issue? I've been adding a pH up (pH @8.4) so maybe it's related?

I experienced the same thing a few years ago using Marine Buffer. My dkh went through the roof.

 

[Leland Foley]

I experienced the same thing a few years ago using Marine Buffer. My dkh went through the roof.

That's because marine buffer is Sodium bicarbonate or baking soda. It will raise the alkalinity as well as pH.

 

[srad750c]

My API reef test kit said my dKH was 12-13. Is that way too high? Is that an issue? I've been adding a pH up (pH @8.4) so maybe it's related?

I probably wouldn't keep it past 12 dKH, I use Red Sea test kit, I keep mine at 9.5 - 10 dKH, it's 8 - 9 dKH with API test kit. It will come down by itself as your corals use it, then adjust as needed. I use Reef Builder, it doesn't take much.

 

[Roberts reef]

Thanks so much for the info ,just getting into the dosing and am seeing amazing results.