I have four 36W t8 tubes with reflectors over my tank. 2 of these now need replacing as they are beginning to lose their brightness. Are there any cheap tubes I can get that will fit and be ok for plant growth? Are there any better ones I can buy for plant growth without replacing the light units (budget won't stretch that far!)? I am not impressed with the amount of light I get off them so would like something brighter, but I know Juwel are sneeky and make their products so that nothing else fits and you need to buy their own parts! Did a quick google search, but didn't really find much