I have heard mention of wet/dry filters before and again recently. I have only used undergravel filters (a long time ago on a tiny goldfish tank) and i now use external filters. Why are they called wet/dry and what are the advantages/disadvantages?

Normal filters have the water running through them constantly. The bacteria that live in the media need both oxygen, something to live on and the movement of the water. This is why you can have devastating results if you turn your filters for too long. The bacteria are starved of oxygen and running water. A wet dry filter will fill up slowly exposing the media to the air/oxygen. When it's full, it will empty and then the process will start over again. The advantage is that the bacteria get more oxygen than they would in a normal filter. I wouldn't say that any disadvantage with them at all, bacteria need oxygen, and they're getting a lot of it, so in theory they should be nice and healthy and not die off as quickly.

So a wet/dry filter will do the same job as a bigger canister filter?

Also i assume the water level in the tank will vary as the filter fills and empties. Granted not by much?

I expect you are referring to the wet dry filters you have seen commercially available?

A lot of them are referred to as canister filters even though some of them have also got the wet dry facility.

If you've got a canister filter that doesn't have the wet dry facility, the filter will always be full of water. The wet dry canister filter won't always be full of water. The water will trickle through from the tank through the media until it is full, then it will empty back into the tank. I remembered that there is one disadvantage of using wet dry filters, they need to be cleaned more than your average canister. The reason being is if the media becomes clogged, the water doesn't trickle through as fast which reduces the efficiency of the filter. So if you get a wet dry filter, you have to be prepared to carry out maintenance on its on a more regular basis. This is one reason why I stopped using mine. After around two weeks, the filters slowed up. Sometimes it would take up to three minutes, even longer for the filters to fill up and empty.

Think i will stick to my standard canisters

I will try to elaborate on wet/dry filtration. The water level is always at the top of the tank wich i really like. You just have to watch the water level in the filter sump. Now imagine a system where the water falls down a box attached in the corner of your tank, then through a large hose it dumps into the left side of the wet/dry filter. This is the dry side. The water goes through a layer of filter material and is dispersed evenly over a large area of BIO-MEDIA, where all the usefull bacteria grow and mix air and a constant flow of water. The water depth in the system will vary between 6 to 12 inches deep. After the water passes all the media (wich is basically a bunch of plastic balls with holes all through them.) it then passes a few layers of filtration. I personnally have a sponge layer followed by carbon then ammonia gravel then biomax rocks. After the water passes through that whole process it is sucked up by a hefty pump through one inch PVC piping back into the top of the tank. Creating a constant current and water so clear i have only had to vacuum the gravel twice over the past year. I do however change filter components every two to three months. I currently have 3 large oscars, 1 10 inch tinfoil barb, 2 african ciclids, 2 channel catfish caught locally and a buttoned nose turtle. And the water stays clean!!!!

It was originally designed by saltwater aquariums but i find that it does a fantastic job. And at the price i got the entire system i couldn't pass it up. Hope this helps explain things a little better. If i can ever find my camera i will take pics.

That sounds like a sump filter. I thought wet/dry were like cannister filters. Or can you have them in a sump form too. Or are all sump filters wet/dry filters. Remember i know about undergravel, internal and external cannister filters only

Wet dry filters normally do you have a sump. The commercially available wet dry filters can't really have much of a sump because they don't hold much water. Most people make their own sump filters out of aquariums. The one I got will hold around 66 gallons of water.

Normal canister filters aren't really sumps, the water just flows through them. I suppose you could look upon one as being a sump. But really it isn't.

Holly begebees Batman apply the break!!!!!
Wet/Dry filters take many forms some very efective (Bio-Wheels) some not so effective (enclosed in a canister w/d media). Sumps are not filters. Sumps are non-presurized water containers that circulate with the display as a system. We typicaly put filters and equipment in sumps. The most eficient filter typicaly used in conjunction with a sump is a Trical Filter. this is a tower of some kind with fine floss type media to collect debris on the top where water enters. It then drips through a drip plate to be dispearsed over a large media bed. Water then settles in the sump to be pumped back to the display. What makes Wet/Dry filtration work so well is the constant and very large supply of Oxygen to help bacteria consume amonia and nitrites. It's like a supper charger the more Oxygen and fuel you add to the combustion chamber the faster it can be processed.

Wet/Dry filters are not the cure all. They require some maintinence. You need to change the floss and any chemical media just like any other filter. It is recomended thet you flush or stir your bio media when it has to much build up. BUT NEVER LET IT DRY OUT OR CLEAN IT TO MUCH!!!! You don't want to kill the beneficial bacteria. W/D filters do not remove nitrAtes and nitrates kill too just alot slower. You must still do water changes, and gravel vacuming should be done regularly.

I think it's a very good idea to actually illustrate a wet dry filter, especially the one you actually have in mind. Most people have probably seen the commercially available wet dry filters. A lots of marine enthusiasts would probably use a wet dry filter that has a very large sum incorporated into it, this would probably be an old aquarium or something. I have used the commercially available eheim 2329 wet dry filters for a few years and to be quite honest, there are a pain in the arse. There is no way on God's earth I would ever use one of these filters again. I shouldn't be saying this really, a guy who is a member of this website is going to buy my one remaining filter. However, I told him exactly what the score was with them and how much maintenance they need.

Personally speaking, I don't think these commercially wet dry filters all they are cracked up to be. I personally wouldn't recommend one to anyone.

I think a lot of people get confused. Here are two different types of wet dry filter. The second is very similar to the one I will be using, although this is relatively small compared to mine. These type filters normally have a large sump which is extremely beneficial. If your sump is 30 or 40 gallons and you have got a 60 gallon tank, whereas the tank isn't actually any bigger, you got that much more water to play with.

From my experience using the commercially available wet dry filters, I really don't like them at all. They require that much more maintenance to keep them working smoothly. If you let them get gunked up, the water doesn't flow properly. They also don't have much of a sump.