Good Lord! You are only heating your chicks to 95 degrees or so! Hung securely, towards the center of the box at the correct height you will not be burning anything with a heat lamp
I tried a fish tank and it did not do so good for my birds. It messed them up somehow. I like to use wire cages i used one for the first batch and they werre attachjed to me, the second batch i had to use the fish tank and those birds freak out eveytime they saw me, which was a lot. I finally moved them, it helped a bit but they are the most parnoid birds i have and seem to liek to stay away form me where the others coem running.
never again will i use a fish tank
Also McMurray hatchery has a chick care tips page that is helpful with temperature recommendations.
You want to follow recommendations for temperatures and make sure it is hung high enough.
I don't know how big 30 gal. is for a tank, so I am having trouble visualizing it. It should be fine for awhile, until the chicks are bigger.
Also make sure you give them bedding so they don't get spraddle leg. You can put paper towels atop the bedding.
The best advice I can give you is to remember that you can use a 100 watt bulb in the lamp if you are getting them too hot AND they are in your home. BUT it is vital to check your temperatures under the lamp and keep in mind that nighttime temperatures may be lower. So that 100 watt bulb might need to be two 100 watt bulbs for nighttime. I commonly have two or even three (in winter) 100 watt bulbs running for my chicks outside in the brooder or in the garage when it is 10 degrees outside.
100 watts won't be enough for chicks outside or in the garage until they are 6 weeks old and you are trying to transition them to no heat.
Also think safety- hang your light at least two ways not including the clamp so that if the clamp falls off or a flying chicken hits it it won't fall. I use metal wire to accomplish this.