Undergravel filter Vs external filter.?

An external cannister filter is generally better.

A reverse flow undergravel filter would be a usefull backup to the external, you have the gravel there already, so why not pump some water through it and get some extra biofiltration.

A reverse flow (where the water is pumped under the gravel and flows up through it ) works better than a conventional U/G because it doesn't collect gunge under the gravel over time.

Ian

There are several differences to what they do and don't.

The under gravel contains more media as it uses the gravel for the most part as the biological part, but this means the mechanical part of the filter is in the tank and periodically needs removing a messy job at best as it means siphoning off the rubbish below the plate.

Also the movement of water over the roots of plants constricts there growth not the best way to grow them. Unobtrusive as you don't have to find the space for something in a cupboard.

Canister, is easy to clean, beyond all else this warrants keeping the canister over under gravel, however some people don't like the idea of changing it every 2weeks - 1 month.

Polishes the water better removing far more of the tiny bits that float around in the water.

Plants grow more easily.

Rubbish is contained in the canister rather than under the gravel.

The gravel still works to a certain extent holding beneficial bacteria however the removal of rubbish is a simple stir it up and let the canister do the work.

Of course this all depends on the loading of the tank if you have just a couple of large fish then a canister is the only way forward, light loading of community fish then either works well.

You have to look at it this way I was using UG filtration 40yrs ago and as time has passed technology has improved and the canister, is a derivation of a sump system which was the other type of filtration back then.

You can use both together. Each kind has its advantages and disadvantages.

The big advantage of an undergravel filter is that it gives you a huge volume of biomedia (all the gravel in the tank will be your filter media).

But they don't work well if you have any kind of fish that digs and moves the gravel around much, such as most cichlids and catfishes, because the gravel needs to be reasonably evenly distributed on the bottom of the tank in order for the filter to work well. Also, if you have a lot of rockwork or other objects (other than gravel) that cover a substantial amount of the tank bottom, the filter's efficiency is reduced.

Undergravel filters are usually not preferred for planted tanks, because the roots of the plants can eventually clog the filter plate.

The other consideration is that for an undergravel filter you need aquarium gravel in the right size range (with grains roughly from one-eighth to one-fourth inch in diameter.)

That's usually not a problem, but there are a few aquarium fishes that need to burrow in fine sand in order to thrive, so undergravel filters are not for them.

hi there i would say use a undergravel filter u know the ones wih the plates u put at the bottom and then the gravel on it and then get an external filter wo u are duble filtering it the underground filter breaks down the fishes poo and then goes in the externall filter from the undergravel filter which is very good to have that is what i have on my tank and i got it tested and they told me it perfect drinking water quality(Y) so i would recodmend you get a undergravel filter plus a external filter so you got it filtered twice which makes it perfect the skimmer is not so good in my eyes as like it dosent suck and filter as good as a undergravel filter and externall filter anyways good luck with the filter system any questions do not hesitate to ask me

have ran both types of filter before and water did stay clear, but now have sand i use an internal filter with carbon inside and have shrimp and a plec to do most of the cleaning up for me my water is cristal clear but fluval is the best you can buy even though i use an aqua one pump and that is brilliant at cleaning but noisier than a fluval.