I don't know if this belongs here (since it's a question about keeping my fish alive) or in the DIY section (since it's all due to a DIY project I'm planning). Mods please move it if you think it belongs elsewhere.
First, some background info. I've had a 67 gallon tank up and running for at least 2-3 years. When I first bought the tank (used), it had no bracing and no lid. I designed a brace and lid when I didn't have any plans for plants in my tank, and didn't make allowances for a light that's as long as the tank - there's just an opening in the middle. Since then I've added plants but am limited to only putting them in the middle area of the tank, and I want to do more. I should also mention that when I got the lid made, my friend welded the lid to the brace so it's all one piece. This means that the lid cannot be removed unless the water level is low - at least below half. Tank measures 48" L x 18" W x 18" H.
Now, the makeover. I went to one of the fish stores in town and was talking to the guy about what my options are for bracing, and he suggested glass and showed it to me on a couple of his tanks, and it's what I want to do for sure if I can work out the details. However, this will mean that I have to drain most of the water from my tank so I can get the lid off, and not refill it until the silicone dries on the bracing.
The tank is quite fully stocked. I've got 7 angelfish (not fully grown yet, the largest ones are 1.5-2" or so), a shoal of 15 harlequin rasboras, a shoal of 9 bloodfin tetras, 5 yoyo loaches, 5 zebra loaches, 7 platies, 2 mollies, and a bristlenose pleco.
Is it a terrible idea to try to do something like this with the fish in the tank? I'm not worried about dropping silicone in the tank - I plan on hanging something underneath the areas I'll be working on in order to catch anything that falls - but I'm worried about whether my fish will survive in a half empty tank for as long as it takes for the silicone to cure. If keeping them in the tank the whole time is a viable option, I would skip feeding them for a day and then do a water change before draining the tank so the water won't accumulate too much waste.
If it's NOT feasible to make them live in a half empty tank for a day or two... I don't have a big enough spare tank to house them all, but I have plenty of buckets (how long could I keep them in buckets for though?)... I also have a 20 gallon aquarium at work that I could move a few fish to temporarily (I'm thinking the platies, if anything).
Any thoughts/suggestions? Scrap the idea and come up with something different?