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Plecos (or at least some plecos) like currents. How do you create that in your tank? Mine is only a 70 litre with an internal Juwel Compact H filer. I aim it at the surface of the water to create turbulance and bring more oxygen into the water, but how would I go about actually creating currents in the water?

(Bear in mind that I have tetras and guppies that I don't want to have sandwiched on the glass).

You can use a powerhead (or other similar pump) to get more water current. Or just add another filter. It's not going to harm anything by adding another filter, it's just a little bit more expensive than the usual power-head solution.

Many powerheads and filters have adjustments to allow them to flow water slowly or more quickly, so you can adjust it to suit the fish that are more sensitive. Some tetras are fine with a bit of current, but neons are well-known for NOT liking a lot water-movement, so if it's neons, they will be unhappy about it. Of course, guppies are definitely slow-water fish.

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Mats

Its glowlight tetras, and I don't think my guppies would mind too much as long as the water wasnt too strong: before i aimed the water at the surface it used to point directly into the tank and the guppies would go right up to it, swimming against the current to see how far they could get (or thats what it looked like they were doing).

How exactly do powerheads work? What are they?

Short answer: A powerhead is a water-pump...

Long answer:
Originally, powerheads were designed for UndergravelFilters (or Reverse Under Gravel Filters), attaching to the lift-tube of the UGF.

Nowadays, they are more often used just to create a current, because most people use canister filters instead of under-gravel filtration.

Either way, it's the same mechanics as you find inside the Juwel filter that you've got at the moment - a small impeller with a permanent magnet fitted, and a "lump" which contains a pair of coils around an iron core, making a electromagnet making the impeller rotate. There is an intake and outlet. The intake will need some form of "basket" or "net" to prevent big things like small fish, gravel or plants getting sucked into the impeller.

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Mats

I presume your tank is a closed system? ie with a condensation tray and hood?

In this case there is little possiblity of enough fresh oxygen rich air reaching inside the tank (for exotic plecs like Leporancanthicus galaxius)

You can provide this with either a good old fashioned air pump and air stone, or with the venturi feature on a modern powerhead. This is a pipe attached to the powerhead that sucks air in and mixes it with the water jet.

I have used these Interpet models. They're not great, but they're OK.



As you probably know, the warmer the water the less capable it is to hold oxygen, so at 85, you will have to pump more air into the system and turn the water over as much as possible to get enough oxygen into the water to support the plec you have.

I don't know what a condensation tray is, but yes I have a hood so all the water is returned to the tank and so yes, I'm guessing this is a closed system.

I was going to get an air stone but the guy at my lfs said they didn't really do any good to the tank. What are people's opinions on that?

To use a powerhead do I just buy one and set it up with instructions or do I need a specific type (sorry, I have absolutely no idea what they really are!). What powerhead should I get (Juwel Rekord 70 aquarium with Juwel Compact H filter)?

A condensation tray is the clear plastic sheet between your lights and the water.

The powerhead shown above is widely available. Buy the PHD 2 model, and set it up as per the instructions, making sure the venturi is set on maximum.

If you can, set the outlet so it's just above the water surface. This will ensure maximum oxygen diffusion.

I disagree with the guy at the LFS. Air pumps are excellent in maintaining a high oxygen concentration. When I turn mine off, you can immediately see the difference in the fishes behaviour.

You may want to consider one if the powerhead is not tolerated by the neons and guppies.

Ok, so the Juwel tank doesn't have a condensation tray as such [My wife has a Juwel 60 and my nevue has a Juwel 70 that I got for him].

Whilst airstones in themselves do not get that much oxygen into the water, the movement of bottom to surface is definitely a very good thing for the tank. The biggest area of oxygenation will still be the surface of the water, but if you keep replacing the water on the surface more often, the water gets more oxygenated. In addition the air-pump is supplying fresh air to the closed system.

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Mats