If your canister filter is putting out 150 gallons per hour, that’s probably about right under the circumstances, sir. Connecting it to the chiller will inevitably attenuate the water flow considerably. Not only is the right angle connection to the chiller a factor, but the water must then circulate through many coils inside the chiller in order to cool it down, and going through all those coils results in a lot of friction and extra water resistance. Your canister filter wasn’t designed for such a purpose and it’s probably doing a respectable job of it, all things considered.
As it is now, the canister filter is turning over the entire volume of your 49-gallon aquarium about three times every hour. That’s pretty marginal — acceptable, but barely. I much prefer to see a seahorse tank being turned over at least five times every hour, so you could certainly stand to step up the water circulation a bit more.
Probably the easiest and most economical way to accomplish the desired result would be to purchase an additional canister filter and install it so that it’s returning water at the opposite end of the aquarium from your Fluval 405. This can be a considerably smaller, hence less expensive, canister filter since it will be connected directly to your aquarium and won’t face the same problem with additional water resistance you are experiencing with the original canister filter right now. Adding another canister filter with an output of 150-200 gallons per hour would put the combined turnover rate of the aquarium at 6-7 times an hour, which should be more than adequate. And it can be an inexpensive canister filter since it’s primary job would simply be to provide better water movement and cross circulation for your seahorse tank.
Best of luck obtaining the desired water flow and adjusting your circulation just the way you want it, Sean!