<a href=showthread.php?s=&postid=10701152#post10701152 target=_blank>Originally posted</a> by hahnmeister
Holmes-Farley pointed out the unlikely science behind Escobal's model. Its not like a bubble is going to be travelling side by side with a protein for 2 minutes before it is finally attracted. There are other forces at play. This is where things get messy.
Randy's model suggests that a bubble attracts proteins, and as the bubble 'dwells' longer, more hydrophobic proteins replace less hydrophobic substances... so in effect, the lesser proteins lose their spot, and have to wait for another bubble.
This is where my interpretation comes in, so take it for what its worth. Okay, so on a shorter skimmer, its a bit like the 'soapy water bubble' analogy... not enough soap in the water, and your bubbles just pop. Since its not like our tanks are laden with skimmate or raw sewage, our 'soapy water' is very weak. On shorter skimmers, very turbulent ones, etc... the bubbles may not attract enough proteins in a low-DOC environment to become stable enough to be collected in the cup. ATI's, for instance, cant skim much more than yellow water when the tank they are put on doesnt have enough protein production (need more anthias!) for the bubbles to collect as they get flung from the bottom to the top of the skimmer. In some cases, where we like to put oversized 500g rated skimmers on 150g tanks (habit from past makers who had inflated claims), the skimmer just doesnt work anymore. Yet somehow, a taller skimmer can. It it that the taller skimmer just allows the bubble to 'build up' a better shell under low DOC conditions? Or, is the taller skimmer just able to attract proteins that the shorter skimmer doesnt have the opportunity to collect at all? I wish I knew. According th Randy, I think he would side with the first example though... as his model pretty much says that the taller the skimmer, the more hydrophobic the proteins will be built up on the bubble. Escobal hints that 'rarer' or harder to collect proteins might need the time. Either way... both examples would seem to agree that a taller skimmer would be better, esp in lower DOC conditions. Sure, the counter to more height would be more air, but if all the bubbles just pop when you hit the neck... what good is that? To skim the harder to get proteins, you would in effect have to add more of the easy ones to create a stable head so both can be taken out.
This is why I started experimenting with vodka dosing on my low DOC system. Im encouraging the nutrient uptake by bacteria, and producing more 'substance' for my skimmer to work with.
Other things I will point out though... this would be the major argument for recirculating vs. single pass skimmers. IF height isnt available, and there are certain 'harder to get' proteins in the water... then keeping the water in the skimmer longer would seem to be a good response. Rather than continuing to pass it throught he skimmer too fast for anything to be collected time after time... slow it down, and let the water get 'scrubbed' harder.
Also, the longer the water stays in the skimmer... the more the ORP is buffered, and the pH raised. Now, we have all noticed on our systems how certain times of the day (usually night) seem to make more of a difference with skimming. So the prolonged exposure could be responsible for some chemical 'restructuring'... chemicals that otherwise wouldnt be skimmed might now be skimmable due to the chemical change of a longer time being blasted with bubbles.
As to what 2 minutes really means... who knows. It could mean that even with a very short skimmer, leaving the water in for that long (so a water exposure time) would be ideal to get out more 'stubborn' substances... Randy might side with that more. Or, could it be bubble dwell time? Well... Randy pointed out that its not like the protein and bubble are side by side the whole time... its an instant attraction, and if things stick thats it. Its not like the protein is going to be 'nearby' for 120 seconds and then 'make up its mind'. My interpretation would be that some DOC's just need to be in contact with the bubble for that long before they have a strong enough contact bond to go throught the collection process in the neck, drainage, turbulence, other bubbles, etc... and make it into the cup. OR, as Randy suggests, perhaps its that with longer dwell times we are actually just getting more of the easier to get proteins onto the bubbles so they are more able to be collected... not the more stubborn ones.
This would explain becketts somewhat. Short dwell time, but rather than trying to make the most stable bubbles, the beckett just tries to collect as much as it can and put it into a column of water.... a tall and narrow column without waterflow... just a huge head of foam. This huge head of foam drains like normal, but its production rate of foam is higher than the bubbles can pop... so proteins that get stuck in the head have a hard time draining out. Speculation 100%, but educated guess based on various theories. Rather than trying to maximize the dwell time under the water, try to maximise the dwell time in the foam head... adding more bubbles faster than they can drain.
Either way you look at it, thats why I say, they all pretty much agree on one thing. It may be overkill, but the best skimmer would be one with not only decent air throughput, but a decent height as well, and a recirculating/counter-current design.
I would add that the cone might be a way to get needlewheel skimmers to behave more like becketts... a large sorting area at the bottom with the large part of the cone (or 'black box'), yet a tall and narrow head up top for keeping a high bubble concentration in a small area up top, like that 'black box' has when you put a 5" cylinder at its top. A skimmer with a 8" diameter base has a hard time keeping that kind of bubble density at the top like a beckett without a reducer very low on the skimmer, as the top is also 8" in diameter. A narrower cylinder can make sorting too hard, and so a smaller pump is used... so next to a big fat box at the bottom of the skimmer, and a low transition to the reducer, the cone may be the next best thing. And then you get the nice smooth transition from bottom to top that wont disrupt bubbles on the way up. Thats why I want to try out the ATB cone skimmers... it will fill in some questions I have about skimmers in general.
in Germany... the Krauts are using best skimmers and make many waterchange...
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