Skimmers

[Bob I]

Originally Posted by Samw

http://reefkeeping.com/issues/2005-08/eb/index.php

"Figure 1 shows the oxygen dynamics of Tank 1 in operation without a skimmer. Figure 2 shows the oxygen dynamics of Tank 2 with a skimmer in operation."

"I had assumed (wrongfully) that oxygen was maintained at high levels through the use of two powerheads that agitated the water's surface. However, once the lights went out and photosynthesis stopped, oxygen levels dropped quickly from a high of 78.7% of saturation to a hypoxic low of 16% of saturation. "

Notice the skimmer took the tank from 16% to about 80+% with only the addition of a skimmer and all else constant in Tank 1. In Tank 3, the tank wasn't oxygen starved at any time so it was more difficult to see the effect of the skimmer since his tank was never low in DO even at night. It would have been useful to see the effect of a skimmer on a large tank that has a low DO level at night.

I think some people have low DO levels at night and never know it. It seems that clownfish can survive at 16% for some time whereas I'm quite sure angels can't. This explains why I've lost angels the morning after I forgot to turn my venturi back on in a skimmerless tank.

There you go, you have the figures, but unfortunately natural laws in the world do not support them. Gas exchange at the water surface occurs due to surface agitation period That is how it happens in the oceans, which do not have skimmers BTW.
As far as Angels go, I have a Heraldi now, and have had many in the past. I have a small tank without a skimmer, and have never had an angel gasping for air. Let alone lose one.
Unfortunately this argument will never end because you have your beliefs, and I mine. As long as I am successful I will never change.

[Samw]

Come on Bob. No one is arguing that oxygenation doesn't occur at the surface. That's what the skimmer does. If you are going to say that the skimmer doesn't add oxygen to your tank, at least have a way to back it up by having some measurements before and after. If you can measure your tank before a skimmer is added and after a skimmer is added and show that it doesn't raise a tank's DO from a low level to a high level, then you'll have a point.

If you think that I am saying oxygenation does not occur at the surface, then you are arguing for the sake of arguing since that is not what anyone (myself nor Eric) is saying at all.

You can have an Angel in a small tank without a skimmer of course. There is more than 1 way to oxygenate a tank. Just because you can keep a whole angel in a small tank without a skimmer doesn't mean that skimmers don't oxygenate tanks.

[Bob I]

Thinking about it I have come to realise that there is surface agitation inside a skimmer. If the water that has been agitated gets into the tank, I will have to graciously admit I was wrong.