boiler shell and tube setup.

[moe777]

hello. first the pool im working on is a 9500 gallon im working on a wall mounted boiler htp 170kbtu boiler. with a 155k shell and tube heat exchanger. the company that sold this kit to my customer says that the system should heat this pool in 15H with no problems after 7h the customer saw 1F temp increase with the boiler full out. his orignial pool pump was 80gpm with no flow control so he picked up a 28-80gpm pump that we can adjust the pump rmp to match a flow rate. the shell and tube (https://alfaheating.com/products/sp-155kti-s) this is the heat exchanger that was sold.
after calling alfa today he thinks we should get a 210k or 300k btu heat exchanger.
the problem:
the boiler is set for 180F with the boiler pump at mid speed and pool pump at 60gpm im getting 6F TD on the boiler side and the pool side of the heat exchanger. 75F pool water temp. in my opinion this will never heat the pool. if slow the pool pump to 600rpm/28gpm. and throttle the pool pump outlet to 90% closed il get 15-20F TD across the boiler side and pool side with 100F water going into the pool. that to me makes scene. only... the pools not getting filtered not can the chlorine system work as its not sensing flow...
what is a good feed temp for a pool water inlet to get 88F pool temp? also what soft of boiler water TD should i be getting most HVAC stuff i work with is 20-23TD.
i could be wrong but i think i have 2 problems #1 the surface of the 155 is to small and cant pick up heat due fast flowing pool water. #2 the 155 might be spec for 13k gallon pool but under perfect situation with an indoor pool in cali.... there fore needing a 210k-300k btu unit. (seeing as the 210k btu would or should absorb all the heat given to it but the boiler to the pool water/ i dont want to over size the shell and tube or under size it. with all that said. he was quoted a 200k btu dedicated pool heater for that pool and that to me tells me i should go with the 210k unit.. sry for all my rants here.