baker.shawn

Yep, actual experimentation with low to very low bioload and high to very high system volume would be interesting. As I stated above, this idea is what made me start looking deeper to begin with, being an engineer myself (albeit a civil engineer vs mechanical or hydraulic). The one thing I can't get over is the stated required high contact time for some organics to attach to the air bubbles. This appears to be the controlling variable.

Actually the 2 minute contact time is a little concerning to me because the skimmer I chose for my 75 gallon set up has a little over 6.5 times the recommended turn over rate and is less than half of the recommended 4-foot height. I'm not sure this skimmer (which is the right size based on the manufacturer's recommendation) is capable of producing the required 2 minute contact time. Which either means (1) manufacturer's of venturi skimmers find a different way to provide the necessary contact time for these organics to attach to the air bubbles, (2) the manufacturers disagree with Escobal's derived formulas, or (3) the manufacturers of venturi skimmers simply have decided it's too hard or expensive to provide the necessary contact time and are willing to allow the more stubborn organics to remain in the water.

As far as the other part goes, there's no need to feel bad...misunderstanding happen. I'm just glad we're able to see it as a misunderstanding and continue our discussion. After all that's what forums like these are about, sharing information so we all learn.

Blake

I'm not sure (I'd have to re-read the links you guys posted) but doesn't Escobal give some kind of purity factor which indicates that water that is skimmed over and over again (some already skimmed some not) gradually gets cleaner and cleaner until it reaches some purity factor of 9.2 times T/G or something like that...? So maybe the 2 minute dwell time can be spread out as well...? I kind of doubt it, but maybe... I know when I had my Vertex IN 180 running on my 40 breeder awhile back (after a disaster from which I'm still slowly recovering...) it pulled tons of stuff out of the water despite people telling me that it wouldn't. In fact, it pulled nastier stuff out of the water than my previous skimmer. So, while I might have a "bad" skimmer for a different set of reasons, I can testify that there is a fair lack of understanding about just what is involved in slimmer function. I need to look at the dimensions of my skimmer and see what kind of dwell time I should be getting. That would be - perhaps - the most important variable in whether or not I was able to get skimmate. However, I'm definitely WAY over the 2 times tank volume per day ratio.

Perhaps our hypothetical system would require a skimmer with sufficiently long dwell time in order to pull enough stuff out of the water to reach an acceptable contamination level. So perhaps that is the driving variable and not the actual system volume. Also, I noticed that he says a maximum of 2 times system volume/day. He doesn't say that is the minimum so perhaps our hypothetical system would skim very efficiently for a short time period, then cut back off, and repeat due to the skimmer efficiency... So many ideas right now. I should probably wait 'til later in the day to post so that I've had time to process all of them. Anyway, more to chew on.

I think you've struck on the key to using Escobal's equations. I did a few more quick searches and the "purity coefficient" is described as the the coefficient required to achieve 99.99% clean water. I wonder, as you did, if you start with cleaner water or dirtier water how does that coefficient change, if it indeed does change.

As far as using Escobal's equations to check the efficiency of venturi skimmers, I found one source that suggested the flow through a venturi skimmer is established by how much flow is necessary to suck air in at the venturi. So it would seem manufacturers of venturi skimmers are more interested in achieving a specific water/air bubble ratio (Escobal seems to set this at 13%) than in keeping turn over below 2 times per day. This source also stated that Escobal's equations are for air driven skimmers and don't apply to venturi, beckett, etc type skimmers. Although anybody can post anything on the internet, and I don't know if there is actual data to back up these statements.

Honestly, knowing what I know now, I probably would purchase a counter current recirculating skimmer rather than the style I bought. Seems to me the counter current recirculating skimmers allow for the highest dwell time possible without building a monster tall air driven or beckett style.

Blake

Some more interesting reading...

http://reefkeeping.com/issues/2002-0...ture/index.php

Can't go through it all right now, I'm at work, but I've lightly skimmed the article and it seems to answer a few of my questions about venturi skimmer efficiency...ie they're not as efficient "theoretically" as air driven counter current skimmers, but they still work.

Blake