Why do a lot of reefers keep a lower alk in their tank (8-9)?

[glb]

I’ve been reading posts about alk for a while and seen some polls about it, and it seems that most reefers keep their alk between 8-9dkh. I’m still dialing in the alk of my 40g and was curious about reasons this range is so popular. Instant Ocean mixes at 10dkh so I was keeping my LPS/softie tank in that range, but wondered if a lower number might be better for some reason. I trust the R2R experts to point me in the right direction!!!

 

[dwest]

Many keep around 7. Especially sps low nutrient tanks.

 

[Podworski08]

Others correct me if I’m wrong but this is how I understand it- ALK should have a direct correlation between Mag and Cal numbers. If Mag and Cal is high the ALK should be kept higher and vice versa. The biggest thing, whether you keep your ALK high or low, as with anything in a reef tank, is to keep it consistent and properly acclimate any livestock going into your tank. Everyone seems to have success in this hobby at all different water level parameters, within in reason of course. Just keep it consistent.

 

[Nicholas Dushynsky]

7.7 for me, you need to add a few lower votes than 8

 

[Righteous]

Your poll doesn’t go low enough. I keep mine at 7.4

It seems that in tanks with low nutrients (like nitrates and phosphates), that high alkalinity levels result in corals calcifying faster than they can generate tissue.

Natural seawater also tends to have very low nutrients and alkalinity of 7dkh

 

[drawman]

7 here also. I feel that you have a larger margin of error with acro tanks at a lower level. I don't run a low nutrient tank either.

 

[Earl Karl]

Alk. levels correlate with nutrient levels.

If you want fast growth, you want high alk. like 12 dkh, PO4 of 0.12 ppm and NO3 of around 2 ppm.

If you want the best colors, you want low alk. like 7 dkh, PO4 of 0.03 and NO3 of <1.

 

[Righteous]

Levels below 7 can start to cause stress, though there are very successful tanks with even 6.5 dkh. At this level though it’s important to be able to monitor and maintain alkalinity stability. Higher levels give a lot more wiggle room, hence why a lot of people maintain elevated levels.

 

[Earl Karl]

I keep mine at 9-9.5 dkh for a happy medium.

 

[motortrendz]

Mine is about 10.5, I keep my po4 about 0.10ish and nitrates are about 4. I have amazing growth and color.

 

[Jay Z]

I run triton other method, Keep mine around 8-8.2 to keep everything in check.

They recommend 8, but I've found my clams look happier at 8.2 with the elevated calc and mag. Didn't notice any ill effects on anything else.

 

[fcmatt]

I was also considering this lately as well. I like io salt. I dislike the high alk. I was considering fritz salt because of that. I will have to start dosing soon versus just water changes. I like alk around 8.5. Maybe as high as 9. Even though being like natural seawater which means lower is also appealing.

I want water changes to be easy without adjusting it. My hunt continues.

I am not a fan of having super high alk. Just feels unnatural to me. Growth is not my biggest concern.

 

[Nicholas Dushynsky]

I run at 7.3 to 7.7 as I use NSW so I dont want to mess about with levels of my new water.

 

[C. Eymann]

When running Zeovit I ran mine at 6.8-7.0

Otherwise, generally recommend 8-9, NSW is usually ~7 but I like that extra degree or so of buffer room.

Nothing wrong with keeping 9-11 IMO just have to make sure nutrient levels dont get low.

 

[homer1475]

I use IO and keep my tank at 7.5.

Lower ALK in IO is simple, but requires a bit of easy math and muriatic acid.

easy peasy math.....
Water volume x Decrease in ALK x 0.123 = Muriatic acid to add in ML

Example:
30G water volume with a 2.5 DKH drop(typical for me and IO)

30 x 2.5 x 0.123 = 9.2ML

 

[Randy Holmes-Farley]

Here’s my alk blurb from one of my articles, including pros and cons of different alk levels:


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.

 

[Sinibotia]

I keep mine at 7.5 because I literally can't make it go higher lol. But so far, in the early going, my corals are doing great so....

 

[ca1ore]

Trident says my alk is nominally 9.5; Hanna says it’s 10.5 ..... whom to believe ....

 

[Scubabum]

I use IO and keep my tank at 7.5.

Lower ALK in IO is simple, but requires a bit of easy math and muriatic acid.

easy peasy math.....
Water volume x Decrease in ALK x 0.123 = Muriatic acid to add in ML

Example:
30G water volume with a 2.5 DKH drop(typical for me and IO)

30 x 2.5 x 0.123 = 9.2ML

Great information. Thanks for sharing!

 

[jelee01]

Many keep around 7. Especially sps low nutrient tanks.

Me.