The obvious reason, to me, why it wouldn't work terribly well is that, in order to provide enough light for growth of outdoor plant seedlings, the fluorescent canopy would normally be sitting directly on top of the seed tray, once germination has taken place. (The seedlings may even touch the fluorescent bulbs; it doesn't harm them, since the bulbs are not hot.) One would then raise the canopy upwards as the seedlings grow, simply to give them the vertical space they need. And nothing is more important in growth of seedlings than adequate light.

Unless you do some modifications to your canopy, I'd guess it is designed, as per norm, to sit on top of the aquarium, right? You'd either have to raise the trays, or lower a shorter set of lights down into the aquarium in order to make an effective seed-starting table out of it.

So, I'd question using the aquarium for growing.... but it could be useful for germination, if you set a tray (or trays, stacked with some space in between) in it, and kept it covered to preserve high humidity. Once the seeds germinated though, you'd have to provide light (but not until then).
Hope this helps, assuming I'm interpreting your set-up correctly.

The other thing I meant to mention (or perhaps to stress) is that it is only prior to germination that seeds require humid conditions. After the seeds have germinated, you want to provide open air circulation - another reason why an aquarium would not seem to me like that great of a set-up for growing.

I agree 100% with abgardeneer. Save your fish tank for starting cuttings. Al

Mine works great.The only difference being, mine has a shop light sitting on the top.I just prop things up or move them down as needed.Never have a problem with humidity.

Here is a link that might be useful: {{gwi:213899}}

This answers a question I was asking myself and others all winter! I picked up a little 10-gallon at a yard sale last year, with intention of doing some sort of plant-starting in it. My friends have a 20-25gallon they are not using, and it has a wire canopy I can set a light on top. Now I am trying to figure out how to Mickey Mouse one light over both of them. Because we rent, I do not want to be drilling holes in the ceiling for hanging. The other attraction is that if the plants are IN the tanks, my meathead cat will be less inclined to play with them, lie on top of them and other things cats do.
So, Thanks for feeding my idea!
Triple_b

triple-b
I also have a 20 gallon that I used to sit on a table by a window,with no added light.I left the gravel in it and sat pots of seed on top of the gravel so there would be good drainage.That worked great also.

Thanks Molly. I just bought a flourescent ballast and two tubes so as soon as I figure out setting the ballast ABOVE the tanks I will be off to the races. I can rest the ends ON something but I have to figure out the height, stability ect. Brain push-ups.

I am currently using a fish tank for my seedlings once they have sprouted, actually, and they are doing great. I germinated them in a prop. tray on a heat mat. At the first sign of sprouting, I moved them to the tank, which is equipped with a light kit. I put two 40w UV lizard lights into it that were compatible. They are marked "Day" at the pet store. It stays nicely warm and slightly humid (I leave the top up) and the seedlings are growing quickly, and the light is perfect. I could have done my sprouts in there, too, it's warm enough, but I wanted to have two separate stations. Once they get bigger I plan to buy another lizard light, this one a clamp-type with another UV bulb, and set them out on the counter with the light pointed towards them. I think this will work just fine til it's time to harden them off--I'll let you know.
AS

Is a lizard light something to keep a pet lizard warm? Al

Lizards, being cold-blooded creatures, cannot produce their own body heat. Therefore they need the a special heatlamp for them to rest under several times a day to maintain body temperature.