Since the ballast in your hood is broken, you can just cut off the cable and tape up. I also used to have a 50 litre tank that I changed the fluorescent tube for the same make LED, but with that the cover of the light ballast could be removed. So I removed it and carefully undid all the connectors, labelling them as I removed them, then pushed the cover back on. When I sold the tank, I reconnected the cable and put the fluorescent tube back.
I have just taken the LED for this 50 litre tank out of its box and photographed it. It is a lot smaller than the ones you'd need for your tank
I took the end cap off one end so that you could see both the end of the tube and the end cap more clearly. As you can see, the end cap is a plastic sleeve that slots over the end of the tube and has metal pins which slot into the the fluorescent tube holder, or whatever it is officially called. It has a power cable coming from one end, and it plugs into the mains via a transformer.
I found that the two tubes on my 180litre tank caused problems with an analogue timer, the kind that have segments round the edge that you push down for the 'on' time, but they work fine with digital timers.
I was lucky because I found these lights in a not too local shop so I was able to see them, and in action on their tanks, before I bought them. When I got mine there were two types - bright white and colour plus. The colour plus turned everything orange so I bought all bright white. I think they do a third type now with mixed colours.
And I think they now also do a version with T5 end caps as well as T8.