Deeper is Better
Deeper is Better
All bubbles have a propensity to attract hydrophobic compounds and repel hydrophilic compounds. You will not find different bubbles such that one is more attracted to surface proteins and another is more attracted to yellowing compounds. All bubbles will be more attracted to surface proteins than “Gelbstoff†or “Gilvin†or chromophoric dissolved organic matter (CDOM). All bubbles will repel hydrophilic or polar molecules.
Let’s take your 4 compounds (A, B, C, D), of equal concentration but different solubility such that on the solubility scale, less of A will dissolve in aquarium water than D (A < B < C < D).
• Compound A will quickly bind to a bubble and be removed by the skimmer.
“Nearly any hydrophobic or amphipathic molecule can be skimmed out to some extent. This list includes amino acids, vitamins, proteins, carbohydrates, fats, many combination biomolecules (e.g., lipoproteins, liposaccharides), RNA, DNA, etc. This list includes most, but certainly not all, organics. Fortunately, it includes many of the organic compounds that lead to yellowing in marine and reef aquaria, so skimming can help reduce the yellowing of aquarium water.†- Randy Holmes-Farley (
http://reefkeeping.com/issues/2006-08/rhf/index.php)
• Compound B may bind to a bubble only to be replaced by compound A as the bubble rises.
“Additionally, different organics have different binding strengths to the air/water interface. Compounds which bind more strongly will slowly replace those already at the interface which have weaker binding. Thus, a bubble which is completely occupied with organics might still be changing with time upon further exposure to aquarium water.†- Randy Holmes-Farley (
http://reefkeeping.com/issues/2006-08/rhf/index.php)
• Compound C may take two minutes of contact time to bind to a bubble.
“Some organics require up to 2 full minutes of contact time with air bubbles in a skimmer before they are removed via foam fractioning.†â€"œ (
http://www.hawkfish.org/snailman/skimmer101.htm)
• Compound D may never bind to a bubble
“Most highly polar organics will not be removed by skimming. Simple sugars, acetate, oxalate, methyl alcohol, choline, citrate, etc. will remain behind. They simply are not sufficiently attracted to an air water interface. Most charged species are, in fact, repelled from the air/water interface, so they are not collected. Fortunately, many of these highly polar organic materials are readily metabolized by bacteria and other organisms, so they do not continually build up in marine aquaria.†- Randy Holmes-Farley (
http://reefkeeping.com/issues/2006-08/rhf/index.php)
Conclusions:
1. All skimmers will remove compound A better than compound B, B better than C, and C better than D.
2. Skimming “deeper is better:â€Â
• If a skimmer can remove B, it will also remove A.
• If a skimmer can remove C, it will also remove A & B.
• If a skimmer can remove D, it will also remove A, B & C.
3. “Shallow skimming is worse:â€Â
• If a skimmer can’t remove C, it can’t remove D.
• If a skimmer can’t remove B, it can’t remove C & D.
• If a skimmer can’t remove A, it can’t remove B, C & D.
If Randy is right, we may not need a test kit to measure CDOM (C & D). Maybe a color card is all we need.
Bottom Line:
Popular skimmer designs are based on rapid removal of surface proteins with large air to water ratios in order to impress uninformed aquarists with the amount of foam generated and the amount of skimmate collected. Their tanks still look yellow with chromophoric dissolved organic matter (CDOM) and require ozone, carbon or water changes to be presentable.
“A fool and his money are soon parted.â€Â