Oxygen is critical at night when no photosynthesis. Opposite photo period helps. It is critical that your water surfaces provide good gas exchange. To that end, surface tension needs to be eliminated with a surface overflow skimmer weir that removes any organic skum. Aggressive circulation at the surface breaks surface tension.
The claims of superior oxygen exchange with skimmer operations are exaggerated. The physics of surface tension at skimmer bubbles provide the mechanism for skimmers to export nutrients. Due to the same physics of surface tension, gas exchange is severely limited.
I am just an engineer, but I study the sciences.
Patrick
PS. Your sponges feed all the time. On the natural reef, most filter feeding is done at night when zooplankton is abundant. That is when I would turn off the skimmer.
How did you evaluate 50 GPHr? I think it may be a lot more than that. Your picture of your skimmer shows clean bubbles. How can this be in high nutrient tank?
Patrick
Ok well i'll try to explain and answer some of your questions
First when i designed the system i had some engineering notions. On both the 75 G refugium and 150 Reef tank have a coast to coast overflow for skimming. And nothing, none of the little square boxes or half moon corners that most tanks have can match the 6 feet and 4 feet skimming weir i have thats for starters.
The custom reef tank overflow and the custom external wavebox i've had put in, for $20 more .
The refugium external coast to coast overflow , are the most efficient .
Second my system has a total volume of 230 Gallons and my Reef Octopus skimmer is rated for a 300 gallons. So its a good ratios, and a fast extraction.
Both tanks have their own herbie drains system that goes to the sump and their own individual independant return pumps.
The refugium feed the reef via a 1" flex 1 inch below the waterline , so not to get the skimming junk that the overflow is suppose to get. The connection gets the pods and other critters.
You where talking about oxygenation. My Orp is usually between 370-450 depending of the time of day. Its higher at night because during the day the fish are active and so is the rest of the tank, at night everybody sleeps except some of the CUC.
My 5 Tunze pump also disturb and break the surface of the 3 tanks, the reef, the refugium and in the 65 G sump i have a small pump as well to make ripples.
It is a high nutrience tank because i dose for;
sponges
NPS
Gorgonians
clams
my macroalgaes
And its primarily a softies and LPS tank. And dosing lots of these supplements make it a high nutrient tank, not at all for SPS. Anyone who ever kept NPS will tell you that.
But the skimmer and the design of the tank is so efficient its extracting too much, even what i'm dosing or putting in. Thats why the turning Off question rose after i saw some tanks and watched some on YouTube not having the benefits of Skimmers.
I'm not giving up my skimmer, i don't think my tank could survive without one, but having lost 2 sponges to starvation its an option i can't neglets. Its the logical option to try anyway, with a 24/24 skimmer its dying so with a reduced time frame we'll see the result after a few weeks.
Beside's i've been maintaning my gorgonians and NPS, but i haven't see any growth really, with that maybe i'll see some. Its worth a try.
As for sponges studies in many article are suggesting 1 cubic cm of sponge matter filter 4 liters of water a day. From the number of sponges i have and their volume i've estimated their filtration capacity to 50 GPH thats lots.
Finally Sponges have minuscules pores, too small for zooplankton , they mostly feed on bacterias and small and i mean very small phytoplankton. Bacterias that is contained in "poo" is actually ideal apparently and if removed too quickly well the sponges have a very lean meal and so is are sea cukes, lol.
See sponges ; Wiki;
http://en.wikipedia.org/wiki/Sponge
Particles from 0.5 μm to 50 μm are trapped in the ostia, which taper from the outer to inner ends. These particles are consumed by pinacocytes or by archaeocytes which partially extrude themselves through the walls of the ostia. Bacteria-sized particles, below 0.5 micrometers, pass through the ostia and are caught and consumed by choanocytes.[3] Since the smallest particles are by far the most common, choanocytes typically capture 80% of a sponge's food supply.[14] Archaeocytes transport food packaged in vesicles from cells that directly digest food to those that do not. At least one species of sponge has internal fibers that function as tracks for use by nutrient-carrying archaeocytes,[3] and these tracks also move inert objects.[4]
Sponges' cells absorb oxygen by diffusion from water into cells as water flows through body, into which carbon dioxide and other soluble waste products such as
ammonia also diffuse. Archeocytes remove mineral particles that threaten to block the ostia, transport them through the mesohyl and generally dump them into the outgoing water current, although some species incorporate them into their skeletons.[3]
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