Flow, alkalinity and par

[Flippers4pups]

Very interesting study on the relationship of flow, alkalinity and light intensity (par) and its effects on coral health/growth. Taken from MACNA 2016. Speaker Dana Riddle.

https://youtu.be/fBktpJ3umAs

[rushbattle]

Just to clarify, Dana is assuming that increased rates of photosynthesis are directly correlated with growth rates in corals. This might not be the case in all situations. For example, the corals also need N and P, and corals and their zooxanthellae have preferences for the sources for each. How much energy, mostly harvested through photosynthesis, it takes to grab the other nutrients necessary for growth will likely modulate growth rates.

[blasterman789]

Ditto.

Measuring the degree of photosynthesis has nothing to do with how well the coral is growing. Just means it's converting sugar.

[2smokes]

I dont agree with ,,too much light can be detrimential,,.If you measure the sun light you will discover that at least 10 times more strong than most powerfull lights we use .I dont believe that somebody can ,,burn,, a coral with just a few led lights .The acropora burned tips that he says are burned because too much light -you can see that there is a shaded part of a the coral thats dead also.It has to do with too high alk .Keep the alk as the sea level not higher and the corals should be ok .We dont need to force acropora to grow fast because these corals allready grow fast in normal conditions.He did somme interesting experiments thogh and il look further to the next one with bleaching corals.

[hart24601]

I dont agree with ,,too much light can be detrimential,,.If you measure the sun light you will discover that at least 10 times more strong than most powerfull lights we use .I dont believe that somebody can ,,burn,, a coral with just a few led lights .The acropora burned tips that he says are burned because too much light -you can see that there is a shaded part of a the coral thats dead also.It has to do with too high alk .Keep the alk as the sea level not higher and the corals should be ok .We dont need to force acropora to grow fast because these corals allready grow fast in normal conditions.He did somme interesting experiments thogh and il look further to the next one with bleaching corals.

It's pretty hard to boil down bleaching to a single issue.

Too much light:

There seem to be a few issues that really impact how much light - 1st of all it's can be more about the daily light amount than PAR, it doesn't take a huge amount of PAR if run 12 hours a day to exceed nature. The below article shows that at 500 PAR run for 12 hours a day matches the daily light amount of a Hawaiian tide pool and 525 exceeds it.

http://www.advancedaquarist.com/2013/9/aafeature

pH - with most homes having higher than atmospheric CO2 content this article links lower pH to higher bleaching:

http://www.pnas.org/content/105/45/17442.full

Flow - I can't find the article right now, but our flow in tanks is far behind the average of a coral reef. Extra light energy that can't be used by coral is transferred to heat. In threads where people's corals have bleached flow rate is rarely discussed, but that tiny boundary layer of water around the coral is very important for heat transfer and in wild reefs that layer is smaller do to the much greater flow.

So there are lots of issues that can be related, but at least according to that article we can pretty easily have too much light as in my tank I have areas of well over 500 PAR, after reading that I lowered my photoperiod.

[bertoni]

I agree that many corals (but not all) can tolerate light at very high levels in nature. In our tanks, acclimation is an issue, though. Alkalinity and "burnt tips" is an interesting issue, and I have no idea what might be happening. It does seem that many tanks do better with lower alkalinity levels (7-8 dKH).