Ouachita Dusky Salamander (Desmognathus brimleyorum)

I believe my axolotl is constipated. I got him 8 days ago and have not seen any poop in his tank. I have a 20 gallon tank. No other tank mates. 2 hides and a bare bottom. I didn't feed him the last two days. His belly looks swollen and dark in color. I believe it is the food you can see. I fed him blood worms and soft quick sinking axoloty pellets. I tested his water today. Ph was 7.6. The nitrite and nitrate were both zero. The ammonia was 0.25 ppm. I was advised to cycle my tank due to the lack of nitrate. I added Seachem stability 10 ml to my tank yesterday and 5 ml today. I have a tank chiller. The water temp is set at 64. He is still active, but his tail floats up when he is moving about the tank. I am on the fence about fridging him. I also don't know how long to go without feeding him. I don't want to harm him. Please help asap. Thank you.