Tick Tick Tick Tick

The problem, as I have found, is that LEDs designed for aquariums don't give a K rating 
The one I went for comes in two colours for freshwater - bright white (which is white) and colourplus which is pink and is designed to "make the reds and blues in the fish stand out" (quote from the shop! They had one on a goldfish tank and the fish were bright bright orange under it). I've read that Arcadia tubes are faintly pink, though I've not seen one in use.

The shop also warned about those LED strips that use adhesive pads to fix them in place - they come unstuck. If you go for LEDs rather than replace the ballast and get fluorescents, get those that can fit into the light sockets or those that use circular clips which go round the tube and screw into the lid, assuming your lid allows for that.
And based on my experience with the little 6 inch LED don't put them underwater, even if they are supposed to be submersible (mine leaked).

I know Steve says to get non-aquarium LEDs as they are a lot cheaper (and do have a K rating) but the problems is finding those that don't use the fluorescent ballast as the power supply - you can't do that as yours is dead.
Any links Steve?

I wouldn't trust suction cups either. I have things fixed onto tiles in the kitchen with suckers and they do fall off. I would only use those tubes that can be fitted into the fluorescent tube sockets (either those with plastic pins as part of the tube or those with detachable end caps) or that use screw on clips.
My 50 litre tank has the fluorescent tube sockets built into the lid so I used the end caps on that LED tube. If I ever put some in my 180, the lid is made differently. The current tubes are held in place with clips screwed to the reflectors and the reflectors are screwed into the lid. The sockets are not supported, the tube hold them up. With this set up I would use the clips that came with the LED and screw them into the holes where the reflectors are now fitted.


It was funny with the leaky one, no shocks whatsoever. I emailed the company and they sent me a new one. They said that the individual LEDs were sealed but they didn't mention if the cable was sealed. And they didn't explain why two of the six LEDs stopped working. You'll find the story here.

The thing that put me off those is that they need wiring to a new ballast. If you are going to fit a new ballast into the lid, you may as well fit a fluorescent one.
And I'd be scared of doing it wrong. Wiring a plug, yes easy. But a ballast, and then waterproofing the lid again? That's why I wanted an LED that had it's own ballast wired into the cable. It's the making the whole thing waterproof again that scares me.

Now you are going to tell me that the ballast can be external!

Why would a tube using LEDs need a ballast?

The LEDs in question CAN use an existing magnetic ballast, they do not have to use it.

As I said, it's as technical as wiring a plug. They come with complete instructions; and sealing the hood after involves putting it back with a squidge of sealant at worst. Mine has a rubber gasket and just clips back in!

Some of them totally bypass all this and use the same sort of method as Arcadia. Just shop around.

The light output of these tubes isn't stellar, but it is about comparable to a similar length T8 tube. If your light fitting has broken, as had the OP's light fitting, I don't see it makes sense not to try; At £3.95, can you really go wrong?

Thank you all very much, your contributions have really given me excellent help in finding the right bulb and the  confidence that it isn't going to be to difficult to rewire the hood.