Elevated dissolved organic carbon and coral mortality.

[SantaMonica]

I haven't read that article in a few years, so it's good to refresh a bit. Figure 5 shows that DOC levels in the aquarium are HIGHER when the skimmer is used, and LOWER when the skimmer is not used. This is because skimmers don't remove (much) DOC, but do remove food particles such as bacteria. Since bacteria are what consumes DOC, the DOC rises because nothing is consuming it:


Also...

Organic carbon in both its particulate and dissolved forms has been called "the soil of the sea" in recognition of its role at the very foundation of the entire marine ecosystem. It is the sustenance of the microbiota in the oceans and the entire marine food pyramid rests on the availability of this fuel source. Greater than 97% of the organic matter in the oceans is in the form of DOC

I was off by 1%

[dtyharry]

In the 2nd part of that article, the piece posted by vannypt, they clearly show that the aquariums without skimmers and carbon have much higher levels of dissolved organic carbon. This is think is mostly due to the carbon because skimmers have been shown to not really do an awful lot. I think it is unhealthy to get into the skimmer debate, best just to show what you can do without one.
Natural processes reduce levels of dissolved organic carbon to 'normal' levels within a short space of time. What a normal level is I guess depends on each aquarium and it's filtration type.
The tanks with carbon had levels of dissolved organic carbon much closer to a natural reef than those that did not.

[Green]

The pros and cons of DOM : http://reefkeeping.com/issues/2004-10/rhf/index.php

[SantaMonica]

I missed the part about them using GAC. So of course that's going to reduce carbon in the water. But it was the part before that... where they used only the skimmer... and the accompanying graph... which showed that doc went up with skimmer use.

Also, about the RK article above... we are fortunate that the "negative" aspects of dom/doc are taken care of by our scrubbers (also, it's important to remember that dom/doc in our tanks is less than on real reefs)...

Nutrients: Removed by scrubbers
Oxygen Levels: Increased to saturation by scrubbers
ORP: Increased by scrubbers
Toxins: Removed by scrubbers (even pesticides are consumed)
Light Absorption: Increased by scrubbers (apparently, via introduction of simple sugars)

[dtyharry]

I have been in contact by email with forest rohwer and he has advised me that they use algae scrubbers on some of their aquaria at the laboratory.
He is going to ask for some samples for dissolved organic carbon analysis. Repeating what I said earlier, his belief is that although in theory the aquaria should have problems due to elevated levels of carbon stimulating microbial growth which in turn kills corals, this does not appear to be happening in the aquaria. They appear to be so efficient at removing nutrients such as nitrates and phosphates etc that the microbes are unable to grow, unlike on a real reef where to a certain extent the supply of these nutrients is limitless.
I have told him that if he requires extra samples there would probably be plenty of volunteers from you guys over in the US!
Lets see what happens.

[Floyd R Turbo]

Just on the surface, the fact that corals are not dying in the scrubber based filtration system seems to confirm that there is a difference between algal growth in an open reef versus in a closed controlled system. Things like these are important to consider. I think you made some very good points regarding the connection between reef algae and coral mortality, even though there were other factors. It seems like the more questions are posed, the more it is clear to me that there really has been no significant study or the current algae scrubber technique. It seems like it has just been passed over has having been done a long time ago, yet many of the conclusions that were made in the past are now known to be irrelevant. I feel that algae scrubbing technology (if you want to call it that) is on the cutting edge, and it's only a matter of time before someone decides to develop a big study of some kind. I just hope it's funded by the right person.

[dtyharry]

I think it is because a well run scrubber is acting like a pristine reef. The fleshy algae grows and we act as the herbivores by constantly grazIng the algae ie weekly cleanings.
This keeps the algae at a manageable level and dissolved organic carbon at a satisfactory level because most of the algae's effort goes into regrowing and not leaking out all it's excess energy.
Happy days!

[Floyd R Turbo]

I think you nailed it. Never thought of the parallel between cleaning the screens and herbivores, that makes perfect sense. That might also explain why a few of my corals (LPS - frogspawns and hammers) open up better when I thoroughly clean the screen, which I have started doing and it makes a difference.