Sometimes half full is more than full

One common discussion between hobbyists is “how you skim? Wet or Dry?”. Most aquarists don’t have strong opinion, probably because the decision between two is not easily backed up by any data. Instead, we just use a setting we are used to – maybe because our mentor recommended one or other when we were staring the hobby or maybe because we want to duplicate methods used by some well known aquarist (an expert even). But which one is better?

Many people will tell you that skimming “wet” (adjusting skimmer so that removes more water together with organics) will result in more net export compared to “dry” setting. This is mostly based on the theory that there is less draining back of dirty water.There are some important points that are ignored, however. First of all, the foam head that is formed inside the riser tube is not really an inactive component. The concentrated foam functions as an elevator that can collect much more bacteria and other particulate organic matter than a more dilute solution. Furthermore, no reasonably designed skimmer will discharge the concentrated surface water. Instead, typically the water exists the skimmer from the bottom. I do not see how any significant number of surface active molecules could travel through high number of air bubbles and less concentrated water to exit from the bottom. After all, skimmers really work because they don’t do that.

But that’s just a bunch of theoretical mumbo-jumbo. There is an easy way to tell if your skimmer works better in dry or wet setting. Tune your skimmer to wet and let it skim for two days. Take a picture and clean the cup. Next tune it to produce very dark skimmate and let it skim the same amount of time. Now bring the water level inside the collection cup to the same level as it was with the wet setting and take a picture. Compare the pictures.

All skimmers I have owned export more organics with dry setting – sometimes much more. Here’s an example how concentrated dry skimmate is:

Skimmate produced by a (broken) ATI Bubble Master in 24 hrs

Filled with tap water, typical wet setting

Of course the ultimate test is how healthy and clean your tank looks. For me, skimming dry has always produced better results.

Tags: equipment, food for thought, Husbandry, nutrients

This entry was posted on Saturday, August 22nd, 2009 at 18:23 and is filed under Husbandry, Ideas and misc. You can follow any responses to this entry through the RSS 2.0 feed.