I was given a tank (a 100 litre Rena). It has a hood with a light (18W).

Unfortunately the light does not work. I am going to try and replace the bulb to see whether that is the problem.

If it isn't and I need a new light unit what should I be looking for? E.g. what wattage is suitable? Are some units easier to fit than others? What about a reflector etc.? Do I need a new hood?

I have set the tank up with filter and heater, but don't have any fish yet. I am completely new to this

Thanks in advance for any replies.

Chances are, if the starter unit has completely packed up, you will need to buy a completely new lighting system. Most light units on 'off-the-shelf' aquariums are built-into the hood. If the aquarium hood is wooden, you might be able to remove the old light unit and rig something up if you're willing to do a bit of DIY.

If the hood is made of plastic and the light unit is moulded into the underside of the hood, the whole hood will need to be discarded. In which case, you would be left with the option of buying a new hood (either a replacement from the manufacturer) or a flourescent luminaire that uses either T5 or T8 tubes.

Luminaires can either be suspended from the ceiling or from wall brackets or supported on the rim of the tank by plastic or metal legs.

Thanks for your reply.

The tanks are no longer made by Rena as I understand it so I can't presumably buy a new lid/light fitting specifically for the tank.The lid is plastic by the way.

If I buy a new unit what wattage should I be looking at? I read yesterday to allow 20W fluorescent per 30cm of tank length to keep plants alive. That would mean a 60W bulb which is 3 times what was originally in the tank. Does 60W sound excessive?

How deep is your tank? Deeper water means light can't penetrate as easily through the water column to the bottom. Light intensity will also depend on what species of plants you are keeping. Demanding species such as Glossostigma require demanding of light, CO2 and nutrients for example.

It's worth keeping in mind that as you increase light intensity over the tank, plants will photosynthesize at a faster rate. As a direct result, the live plants will consume more Carbon Dioxide (CO2). Unless you are dosing CO2 into the water column, any small traces will soon be used up by the plants to the point where it is completely exhausted. Unless you start dosing CO2 once the trace amounts of the gas in the water have diminished, plants will soon start to die off.

You'll find that there aren't many 60w tubes that would be physically short enough to fit over a 100 litre tank, unless the tube in question is a T5 compact.

One or two standard T8 or T5 tubes would be ideal. Take a look at the Arcadia Freshwater T8 tubes, the 24"/18w tubes would probably be the most suitable depending on the length of the tank. You could also consider the Arcadia I-Bars, which simply screw into the inside of a wooden aquarium hood. These are getting a bit thin on the ground now as they aren't manufactured by Arcadia anymore, however you should be able to find one brand new on eVilbay.

I'm also a big fan of the Giesemann Powerchrome T5 tubes, these will fit in any T5 starter unit of the correct size.

Thanks again.

The tank is 40cm deep (by 30 wide and 80 long). Maybe I misread the information about wattage and it was 20W for each 30cm of depth.

I'm going to the shop tomorrow so I'll have a look at what they have. Hopefully a new 18W bulb will do the trick. I might be able to drill into the platic of the hood and fit a new unit if that is the problem. The old unit just unscrews from the hood.

I am not going to start off with plants (or fish) that are difficult to keep so maybe 18W will be OK.