Okay, I'll try.
1. Do you need a skimmer?
Let my give a little info on my situation first. I like to keep a very high bioload in all of my tanks. I have what many would call too many fish and corals in my tanks. After saying that, I feel that a skimmer does help me a great deal. I keep tanks both with and without skimmers and have found that the skimmed tanks are much more forgiving. If I overfeed the tank the skimmer takes care of it for me. I have less algae problems and the water looks cleaner on the skimmed tanks. Not to say that algae problems are non existant but I believe that the skimmers do help keep it from taking over. I am trying to keep a small nano tank without a skimmer by doing water changes but have been having some major problems with algae an sick fish. These problems may be caused by the small amount of water in the tank and unstable water enviornment though. If I could put a skimmer on the nano I would. I also kept my first 29g tank without a skimmer for about six months after I started it and once I added a skimmer the water quality improved greatly and fish loses decreased. In my showtank using the large DownDraft skimmer I am able to feed very heavily and change very litte water without any noticable water quality problems. BEWARE BEWARE BEWARE - Do not take this as a recommendation to overload your tank and not change water like I do just because you have a large skimmer. I use other means of filtration besides my skimmer but I am saying I would not try to keep the load that I have without a large skimmer on the tank.
2. Can I save some dollars and buy something to get by for now, then upgrade later?
I would say no. I have tried this and ended up spending much more money in the long run. My $300 ReefDevil actually cost me $600 because of all of the other skimmers that I threw away. IMO, get the best skimmer from the start and keep the money you save for livestock instead of buying junk that will end up in the garage or trash.
3. Are the manufacturers telling the truth when they say this skimmer is rated for x number of gallons?
I would think that most manufactures are telling the truth based on a specific load. If you have a skimmer rated for 60 gallons on a 60 gallon tank with no fish it has a good chance of meeting your needs. If the same 60 gallon tank is loaded with 12 fish the skimmer may be underpowered. The manufactures do not give enough detail on how they come up with the capacity ratings. I use CPR backpacs (rated up to 60g if I remember correctly) on both of my 29 gallon tanks and one is cleaner than the other because of the differnt bio-loads. I myself like to use an oversized skimmer on my tanks so that I have room to grow.
4. How many types of skimmers are there and what is the difference?
Here are the three types that I have used on my tanks.
Counter current - Most CC's consist of a pastic tube, airstone, and air pump. I have used the small in-tank type CC skimmers and have not had very good luck. I had a hard time adjusting them and the airstones got plugged quickly. I have heard that there are some very large CC skimmers that work very well but they are hard to maintain, need large airpumps and do not look good in the living room. One advantage is that they are supposed to be more plankton friendly and do not kill off the good critters like some of the other types can. Many reefkeepers swear by CC skimmer have very successful tanks to back them up.
Venturi - This is another type of skimmer which uses a powerhead or pump and an air intake to create the foam. The combination of the venturi air intake and the water pumped into the skimmer column creates a large amount of bubbles. These are fairly small in size and work well on most tanks. They are cost effective, come in many different sizes and are popular with many reefkeepers. They are maintained by cleaning the pump every so often and once adjusted are fairly stable once the correct water level in the riser tube is set.
DownDraft - Skimmers of this type are very powerful and skim very well IMO. An extreme amount of water and air is mixed together to create the foam. Because of the amount of water flow needed a very large pump needs to be used. Because of using such large pumps your electric bill will suffer and chances are that some heat will be added to the tank. As far as operation the large pump pushes a great deal of water through a tube of bio-balls. The tube that contains the bio-balls also has an air intake. The amount of water moving through the tube creates a large amount of suction and pulls in a huge amount of air. This air and water mix combines to create a very efficient unit in a somewhat small package. The only disadvantage that I have found is that they are somewhat hard to adjust when first setup but do become stable after time. It is also believed to kill plankton and other small critters because of the very powerful pumps used. FWIW, This is the type of skimmer that I run on my 75g show tank.
There are a few other types of skimmers available such as the HSA which uses a fountain spray jet to create the foam but I have not used these myself. It is said that HSA's work as well as DownDraft's but use a smaller pump. I cannot comment on these because I have never used them.
5. Can I make my own?
I am sure that many great DIY skimmers can be made at a great deal of cost savings but I would just end up flooding my house.
Remember your results may vary.
HTH
Doug
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http://38.222.244.200/dougw
[This message has been edited by Doug (edited 10-26-1999).]