How did you acclimate him? Did you only temperature acclimate or did you do drip?
Just for everyone, you should always drip acclimate. Inverts need quite a bit longer. I do mine for about 2 hours. That tank and set up looks great. Why do you have a chiller? Is is very hot in your home?
I acclimated him for about an hour, but prior to that, over about a week, I adjusted temperature and salinity of each tank to match. pH was the same in both tanks. Basically every measureable paramater was identical save for 5ppm nitrate in the new tank (which was quickly comsumed by the chaeto). Both tanks use the same salt as well, so I felt comfortable enough in a shorter than average acclimation. I used a turkey baster to do a pseudo-drip acclimation. Same thing as a normal drip except I used a turkey baster and stood here for an hour slowly dripping the new tank water in.
A couple reasons for the chiller...
As with most smaller AIO tanks, the pumps are in the back chamber and they tend to generate heat. Add to that a couple powerheads in the display area and you have a recipe for a warm tank in the summer. I like to keep my tanks around 78 degrees and in the summer, we set the A/C in the house to 78. Add heat from the pump and the powerheads and this tank would probably be running at 84 degrees or more.
The previous owner found it necessary to add the chiller, so I bought it from him when he sold me the tank. It was such a screaming deal that I would have been dumb not to buy it.
This tank is about 90% covered on top, so evaporation is almost none. The skimmer keeps the oxygen levels up, but most of the heat stays in the tank. Thus, I have a chiller.
My little 2 gallon AIO tank also needs a chiller in the summer.
My 10 gallon tank doesn't have a chiller, but I'll be adding one before the summer. Last summer, I had to run a fan on that tank 24/7. That tank has an ATO, so it wasn't a problem, but I'd be happier with a chiller on that tank.