Old Halide Bulb causing Diatom bloom?

Any idea how old it is? Or possibly the spectrum of the bulb? It's very possible for the bulb to be growing more algae. Most times when the lower k spectrum bulbs get past their prime then end up more like the 6.5 k spectrum which is perfect for growing.

 

I know alot of people have great looking tanks with led. Alot of those fixtures are the Chinese ones like reef breeders or ocean revive and a few more. Personally I like t5 i run them on all my tanks. I never had good experience with led but everyones setup is different. But it's hard to beat a good old metal halide fixture to unless heat is a problem.
And yes old bulbs will help fuel algae growth and the spectrum shifts and coral color will suffer also. Just be careful when you switch light in or bulbs cause you will shock your corals and possibly bleach them. When I do a bulb change on my 8 bulb fixture I usually do 2 bulbs every 3-5 days and raise my fixture up an inch or 2 so everything can acclimate.

 

Well post what size and dimensions of your tank,what corals are you looking to keep and a price range. There are plenty of mounting options like rail kits and tank mounts or make your own. Maybe some led people will help you out cause they have way more experience than I do.

 

I always thought the aquatic illuminations hydra 52 or eco tech radion pro were the best LEDs out there until I started researching them more. You should look into kessils, the best light they have out right now would be the a360w-e. It's about $400, cheaper than the other "high end" LEDs. They have the best spectrums out of all the fixtures, they produce their own LEDs in house, American company, only true uv led out there, and they have a really slick gooseneck mount. It's the light I have over my biocube which would roughly the same size as yours. If you look up any recent threads with lighting experts that have tried out all other brands they all highly recommend kessil. When switching from metal halide they're about as close to the same "feel" in an led fixture you can get.