your pool holds 17,000 gallons of water (about 140,000 pounds) so you need 140,000 btu to raise your pool 1 degree (not counting the normal heat loss of your pool) from what i can find on the net your model of stove is rated (depending on a few things) for 250,000 (so likley you are near its maximum output)
by your photos it looks as though you may have 3/4 or 1 inch lines from your OWB to the plate exchanger,,,3/4 lines would maybe move 9 gpm and if they are 1 inch perhaps 14 gallons (really pushing it) and your pool lines look like they may be 1 1/4 (if so they could be pushing 21 gpm)
most pools are designed with a pump that will change the pool water 1 time in a 24 hour period that would be about 12 gpm (then again some pool salesmen like to sell you a bigger pump to help keep the pool cleaner and gives more suction to the vacume)
lets say you are pumping pool water at 12 gpm and OWB at 9 gpm...you will cool the water so fast you wont see an increase in the pool water temp (although it is there) and you are likely cooling the return water to a dangerous level
i would suggest you slow the pool water gpm to something low enough that the delta of your furnace water (in and out temps) is no more than 20 degrees. this will allow you to see some difference in the water temps of the in and out of the pool water. it will take longer to heat your pool but it will be better for your stove. also you may consider an aquastat to control the pool temp.
another thing to consider is a pool cover, i have read on the net they can save you up to 25 percent of a heating bill (wood in your case)