Crayfish health

Question
I had fifteen crawdwds to start out with in a 20 gallon aquarium ,and at first they were doing great, although they fought for dominance (normal)Ok so they did good for about a month then all the sudden they started dying off?
My tank temperature gets to the lowest about 81 degrees and sometimes it will get to almost ninety degrees at the highest.
I think the problem there is lighting is getting the water too hot.
My settup is a 20 gall long tank, 2 25 watt incandesent bulbs (on for twelve hrs then off for 12),tank an air pump, quite a few rocks to hide under and about an inch or so of regular gravel.
I feed them some meal worms, a few goldfish that they had caught and started on bloodworms.
To wrap up, at the present time I have 8 crawdad left. I lost about 5 in the last 4 days.
Am I doing anything wrong?

Answer
Hi Tony,
Thank you for your letter. Yes, the temperature is probably too high. Keep it in the mid 70s. Also, your light could be reduced to about 5 hours a day.
Please read and print out my page for easy aquarium care:
http://steamboats.com/aquarium.html
The leading cause of fish loss is over feeding. The crawdads might eat the extra food you put in, but the excess fish waste will pollute the water.
You need a friendly bacteria culture, so use the product "Cycle" to provide organic biology. Also, if you feed live food, you may only need to feed ever other day or every two days.
Please write back if you want to discuss further.
Nori