Tell me why I can't use MH/T5 lighting systems designed for hydroponics?
 

Why can't I do this?
It seems that they employ the same manufacturers and just change the bulbs to be more red. Prices for the fixtures are really cheap, integrated 150-250 Watt systems run ~$120-150. Why not just get a more appropriate lamp and use them?

Same for the T5 fixtures, the bulbs aren't great but the fixtures look pretty good.

Please let me know what the thinking is around these products.

Several of the manufacturers out there make equipment for both the hydroponics market as well as the aquarium hobby.

http://www.sunlightsupply.com/ is one example. I think Hamilton and PFO do as well.

Progressive Reef www.progressivereef.com is a shop in Victoria that sells both hydroponics and aquarium products. They have a sponsor page on this forum and might be able to better answer product specific questions that you may have.

I don't see why this would be a problem. I have a couple hydroponic systems and a reef, and there are only couple of key distinctions. Bulbs, and reflectors. My T5s for my hydroponics have significantly inferior reflectors than those on my reef and the bulbs are totally different (unless you are trying to grow a lot of macro you probably want different bulbs). Other than that, the T5s come in the same HO wattages that I use on my reef tank. One other thing to keep in mind when comparing systems, is that there are quality differnces in the componets such as active cooling, moisture resistant encaps and better quality ballasts that will all raise the price of reef lighting above hydro.

yup, it's the reflectors that are the price killer. The Plant ones will work but you may not be getting ALL the light you can out of your Bulbs. Depends on what you want to keep in your tank

...and how much electricity you don't mind wasting. ;)

cost conscious aquarists
 

we all know aquatic aquarists are in the minority and so anything destined for this trade will automatically be marked up 50% no exception.

Yup. ....its the reflectors. Would probably be fine for a softy tank.

I have two 4' T5 fixtures on my tank with "Blue" bulbs. It gives the nice dawn dusk look. They are sunlight supply. In theory they don't have water proof plugs/end caps and I've heard of people getting shocked easily from them, although I haven't had any problems.

MH DIY Reflectors are fairly easy to make and DIY T5 reflectors can be done as well, although they are a bit harder.

i have a sunlight supply t5 48 inch 8 bulb fixture that was mounted 1 foot almost above the water and it had tons of light comeing from it and i didnt find the reflectors inferior at all even compared to the tek fixtures ecspecialy because every bulb has an individual reflector also. this was on a 90 gallon

the reflectors in hydroponics can be just as good as the ones for tanks, hydro guys are just as worried about efficiency as we are, its just they have alot more cheap low quality ones than we do for aquariums.
you get what you pay for no matter where you shop but hydro guys dont pay the excess premium that we aquariests pay for our specialty equipment.
You can save a bit of money buying a hydro one that is still good quality (dont buy a $20 reflector and expect it to work as good as a $300 one)
but they have a larger market where people usually buy multiple units, so the costs go down due to volume.
Best way is to get some high reflective aluminum and make your own, you can buy a sheet of polished aluminum for fairly cheap and slam a reflector together and copy whatever design works best for you,
or do what i did and buy a cheaper hydro reflector and modifiy it to fit and preform better on a tank shape.