How to Choose a Good Protein Skimmer
As the cost of buying a high-end protein skimmer for home tank now reaches $1.5K and yet there are no quantitative tests to justify its purchase. For this, and for fun as well, I've spent time to study the design principle, practice and evaluated skimmer products on the market for my own benchmarking and decision. This thread does NOT promote/demote any brands nor reveal any product names evaluated, simply provides a summary of what I think an efficient and cost effective skimmer should be and hopefully help fish geeks of this Forum to make a wise purchase decision by the following guidelines.
Principle in layman's term:
Blow bubbles into the bottom of a column of water and fish wastes in the water will be swept away by the ascending bubbles to be collected on the top. More finer bubbles and more bubble ascending time would drag more fish wastes out by this skimming action.
How are bubbles generated:
Bubbles generate by two ways: air diffuser with a air pump on the bottom of water column or alternatively, a venturi tube on the suction side of a water pump.
Pros and Cons:
Air diffuser is 5 times slower than venturi (actual data measured) under same water flow rate in waste removal of the same design but requires no extra water pump to operate and is silent. Diffuser needs to be cleaned weekly and replaced every few months. The high efficiency of venturi bubbler is traded by the NOISY cavitation sound inside the venturi and extra power consumption. High end skimmers have good silencers but it's for tank owners' decibel reduction not for your poor tankmates because silencers are always out in the air. Constant high noise level may stress fish.
In a 5-gallon bucket with 3-gallon seawater add 20mg(2mL of a 1% PO solution) of Palmolive Ultra Concentrate (PO) dish washer detergent, put your skimmer in and turn it on, time it until no continuous bubbles coming out from the collection cup. A good skimmer will take less than 5min to pull all detergent out of the bucket, leaving absolutely no bubbles in the bucket. This bubble-free sate would occur prior to no bubbling in the collection cup. Most high-end commercial skimmers tested passed 10min mark, one passed 5min mark. All high efficiency skimmers are noisy to fish (push my ear to the tank to check) but not to human; most low ends are noisy to both. I also used FW to test efficiency. The FW results are very interesting, to be published later.
Shape of water column:
Best fluid dynamic design is a circular cone,straight circular tube is a near 2nd, do not consider rectangular tube due to dead space and low/no RPM, thus low efficiency.
What is your RPM:
Key to high efficiency of skimmers is a combination of tangential inlet and countercurrent flow design. A new quantitative measure of water cyclone spinning RPM is used to evaluate all skimmer products. Just measure the pump flow (G, in gph, normally 2x or higher of your tank volume) rate, water column diameter (D, in inches at where inlet located) and inlet tube id (r, in inches) with the formula below:
The higher RPM the better( Dyson vacuum commercial?) skimming efficiency, but after 400RPM, diminishing gains is reached with a tubular design.
So hopefully by now everyone knows how to pick a good protein skimmer or concluded as I did, make one by DIY, without the influence of metaphysics
on the Web.