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Let us run through a few examples :
You have a 55 gallon tank, with trickle filter but it does not meet all the requirements outlined in this list, the load is medium, you feed 3 times a week and you plan to use ozone. 2 Poly Filters are used and so is X-nitrate. Your air pump is a fairly recent Schego, and your husbandry techniques are good. You clean all mechanical filters at least once a week : your score would be 26.5. If you were running the same tank without a trickle filter your score would be 49.5.
Same tank but with a heavy load, no Poly filters, and no X-nitrate and you do not really clean your mechanical filters every week : the score would be 42.5, and if you did not have a trickle filter, it would be 65.5 or more.
To decide on which skimmer is recommended for your tank, look at which category your total fits in :
Up to 20 points : short and narrow
21 to 30 points : narrow and tall
31 to 49 points : wide and short
50 or more points : use a wide and tall, or a Venturi skimmer.
If you cannot find a skimmer of exactly the size recommended, it would be wise to buy a size larger than the recommendation. This will ensure that you have at least the amount of skimming that is, in my opinion, necessary.
Another way to use this checklist, is to determine which factors influence the skimmer size heavily, and then make sure you do not fall in that category. For example cleaning your mechanical filters at least once a week, and using ozone, takes a total of 20 points off your score.
Take the number of airstones we recommended into account as well, and remember that airstones need to be changed about every 3 to 4 weeks maximum. This will ensure that they always produce small bubbles, and skim more efficiently.
I strongly feel that a Reef tank needs to be run with a good and properly sized foam fractionator, protein skimmer. My experience, over and over, has been that its use results in greatly improved water quality, higher dissolved oxygen levels, and a higher natural redox potential.
Most Hobbyist will find that the protein skimmer they need will not fit underneath their aquarium cabinet. That may be one of the reasons they resort to either not using one, or using one that is too small. Such will, I feel, lead to problems with water quality, which in turn will lead to problems with the animals, and seemingly uncontrollable outbreaks of micro-algae, parasites and disease.
Skimmers can be hidden in special cabinets placed next to the tank, or if you are in the category that requires only a short and wide type, it may fit underneath a different type of cabinet. You may have to make the special cabinet yourself, or have it made at some local carpenter's work place. Another alternative is to use a Venturi skimmer, because they are smaller and "will" fit underneath the tank. At the time of this writing only 3 types of Venturi skimmers were available in the North American market :
Venturi skimmers tend to cost more money than columnar ones, but you will not need an airpump, and you also do not need air stones. Make sure that the model you decide on can be operated with ozone, as you will probably end up wanting to use it.
Determining the size of the protein skimmer and the number of airstones it should have, is only part of the equation. We still need to determine how much water to flow through the skimmer, and how much air should be used.
For every "load" there is an ideal flowrate, and that flowrate cannot be determined unless you have a redox controller. Since this is not a unit that we will include in a basic set up, we need to look for other ways of approximating that gph,A and end up with an efficient skimmer. To do this, we need a few more explanations about protein skimmers.
As indicated already, the efficiency is determined by :
Contact time of bubbles and water
Size of the bubbles
But also by, in my opinion,
materials used in the construction
shape of the skimmer
actual water level in the skimmer
salinity of the water
use of other additives
Tall skimmer columns obviously result in longer contact times. The water must travel downwards for longer, and the air must travel upwards for longer as well. The combination maximizes contact time.
Equal flow rates through tall and short skimmers obviously result in different contact times. Water should be flowed slower through short skimmers to make it remain the skimmer longer, or it should be flowed faster, to increase the actual amount of times it goes through the skimmer. In my experience the first alternative works better.
As already indicated, wooden airstones are still the best for fine bubbles. Lime wood is my preferred, although oak works better but requires a much stronger airpump, something most Hobbyists do not have. Wisa pumps, however, will blow through oak air stones.
We recommend you use limewood airstones, and change them every 3 weeks if you use ozone, and every 4 weeks if you do not. Although they used to be hard to get at one point, they are now plentiful.
I have also tried ceramic, bonded glass, porous polyethylene types, and although some of them do give off real fine bubbles, they are either not as small as those out of limewood, or you need an extremely powerful air pump, not something most Hobbyists have.
The exact amount of air that needs to be blown through the skimmer is very hard to determine and varies greatly. You may want to use the following guideline : blow as much air as is required to make the whole inside of the skimmer look like a milky white mass of water. Whisper 1000 air pumps, or similar will do the job in most cases. If you need a stronger pump, use a Wisa 100 or a 300, or 2 Whisper 1000's, one on each airstones (combine the output of the 2 air streams of each pump with a Tee and then connect it to each air inlet).
Most skimmers are built using round plastic tube (acrylic). The main reason for this shape, is that it provides an even and easy circular downflow of the water, from the top of the skimmer, where the water enters, to the bottom, where it exits. Circular flow increases the amount of time the water is actually in the skimmer column, and as a result better skimming is achieved.
This is by no means the only shape that one can use. My company makes 12 and 18 inch "square" protein skimmers for very large installation (several thousand gallons), that outperform round models, and cost considerably less. If properly constructed, such units are extremely efficient.
It is, however, a fact that most of the skimmers you will run across , and that you will use, will be round. The water entry fitting should be angled in such a way, that the water is pumped sideways against the inside wall of the skimmer, and slightly downwards. This will ensure that the water rotates, and takes longer to get to the bottom of the skimmer.
Water of a higher salinity skims (foams) better than water of lower salinity. We have little choice over the salinity, as we have to stay within a very narrow range of 1.018 to 1.026 specific gravity. Most Hobbyists maintain their tanks at 1.023, which is also what most authors recommend. The point to remember is that skimming efficiency will diminish if you lower the salinity too much.
The water level in the skimmer determines the type of foam that runs over the top, and into the collection cup of the skimmer. Wet foam, mostly plain water, is not properly skimmed water, and contains much less of the organic and other elements we wish to remove, than a dry foam, that is heavily concentrated, dark in color, and thick.
You must take care to regulate the height of the water in the column so as to obtain dry foam at the top, that runs over in to the cup from time to time. This may not be a one time task, as the way the water skims changes depending on salinity, load in the tank, feeding, etc. Skimmers must be monitored regularly, and adjusted from time to time to ensure optimum efficiency.
The color of the material that collects in the cup should be brown, green, black, or some dark color close to any of the three mentioned. Clear fluid, even if slightly yellowish, is not really what you want. Further adjustment of the skimmer's water level is necessary when that happens. Alternatively, try injecting more air, and/or changing the airstones. Often too, the fitting that you attach the hose to at the end of the airstone may need to be tightened more. If it is somewhat loose, not all the air goes through the wood. Some comes out directly, around the that fitting and forms large bubbles, reducing skimming efficiency.
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