Why is the recommended dKH range higher than natural sea water?

[wwarby]

My LFS recommends a dKH level of 7.0-7.8 and that’s what they run their display tanks on, which are gorgeous and full of LPS, SPS and fish. They’re a widely respected LFS in the U.K. and almost everything they tell me seems to align with what I find out through independent research.

However if you look at almost any parameter list for any fish or coral it says the recommended range for alkalinity is 8-12. As far as I can tell natural sea water seems to come in around 7.3-7.6 in most tests, and the Tropic Marin salt I use creates an alkalinity of 7-8 dKH.

My tanks seem fine at the 7.5-7.8 range I’m shooting for, but curious to understand the discrepancy in recommendations. Why is the average recommendation closer to 10?

 

[Miami Reef]

Read this: https://www.reef2reef.com/threads/question-about-alkalinity-to-randy.932975/

 

[Miami Reef]

From it Randy said this:

I recommend the alk range for a few reasons, but mostly because that’s where reef tanks seem to do best.

Too high of alk is mostly a precipitation issue, and too low of alk may stress corals, especially in tanks where the pH is low too. That’s not a common combo in the ocean.

It seems corals can readily thrive in higher alk and that’s not too surprising, just like they can thrive with other needed nutrients higher than normal.

 

[Reef.]

Some believe higher alk means faster growth, but some claim the growth is weaker, lower alk is said to give better colours…no one knows the ideal tank alk lvl, it’s a matter of picking what you consider the best lvl and keeping it stable.

I aim for sea lvl alk.

 

[wwarby]

Some believe higher alk means faster growth, but some claim the growth is weaker, lower alk is said to give better colours…no one knows the ideal tank alk lvl, it’s a matter of picking what you consider the best lvl and keeping it stable.

I aim for sea lvl alk.

Cool, thanks - I’m gonna do the same as you I think. It’s what my LFS is suggesting, it does sound as though the higher alk recommendation has been arrived at through trial and error by hobbyists but I recognise stability trumps most other things so that’s what I’m aiming for.

 

[homer1475]

I think you'll find most recommendations are actually between 7 and 12.

Most keep their tanks at the middle ground around 8.5. As a new reefer this number gives quite a bit of "wiggle" room as you learn to advance in the hobby.

Over the years of keeping SPS, I have found they do best at NSW levels. I've had less loss, and more beautiful colors(SPS) when I kept my tank around 7.0.

 

[92Miata]

My LFS recommends a dKH level of 7.0-7.8 and that’s what they run their display tanks on, which are gorgeous and full of LPS, SPS and fish. They’re a widely respected LFS in the U.K. and almost everything they tell me seems to align with what I find out through independent research.

However if you look at almost any parameter list for any fish or coral it says the recommended range for alkalinity is 8-12. As far as I can tell natural sea water seems to come in around 7.3-7.6 in most tests, and the Tropic Marin salt I use creates an alkalinity of 7-8 dKH.

My tanks seem fine at the 7.5-7.8 range I’m shooting for, but curious to understand the discrepancy in recommendations. Why is the average recommendation closer to 10?

So - light, alkalinity, phosphate, nitrate, and a handful of other things aren't really independent variables. Corals in higher nutrients can take (and often need) higher levels of light and alkalinity to color up properly. Corals in lower nutrients get burned tips with higher alkalinity faster. It's all complicated and interconnected.

That being said - when the common 8-12dkh recommendation started being used(70s/80s), our equipment was much worse - there were very few powerheads on the market, propeller based designs were 20 years away, lighting was worse, and general coral conditions were basically lower flow, significantly higher nitrates and phosphates, and much higher amounts of white and yellow light.


Nowadays, you have people killing corals because they stripped the water of phosphates - corals dying from lack of nitrogen. Etc. Copious amounts of flow is cheap. Conditions have changed, but reef gospel hasn't. My SPS tank has been between 6.2-6.7dkh for the last month or so. I usually like it around 7.5, but calcium reactors are a bit of a dance - you tune it to keep a set point, growth increases, it slowly creeps down, tune again.

Acros do great at 6dkh in clean water. They do fine at 5dkh too. They grow a little slower, but fine (and frankly, they grow faster in a healthy tank at dkh 5 than they do in a lot of people's tanks ). Frankly, I think they're easier to keep at lower alkalinity, and everything is significantly harder once you get up above about 9dkh. Corals grow faster, but they also crash faster. Growth comes in fits and spurts as they exhaust trace/phosphate/etc - and that leaves openings for algae/etc.