paddow

hi, i have a starite heater that is just finishing its second season,when i discovered water coming out of it. i took the covers off and i found water coming out of the blower. my pool is about 41000 gallons. i have a salt water generator. my chemistry is chl 2 -3ppm my cal is around 150, my ph is constantly at 7.4 to 8.2 my alk is usually 70 to 90. i usually add 3/4 gal to 1 gal per week . and i always pour it in the deep end away from the returns or the skimmers.the pool looks fine but i do have some calcium build up on the gout joints on the tiles.i called starite techs and they told me my chemistry is off.that i probably have corrosion on my heat exchanger. the man said that it is impossable for ph to be 7.8 or 8.0 if my alk is 80ppm. he also told me that ph and alk are the same things. this water has never had a low ph if anything it is consistently high. i've tried several test kits and the ph reading and the alk reading is always on the high end of things. i guess my question is how could my heat exchanger corrode with a higher than normal ph. is it possable to have a low alk ( 60 -80ppm) with a high ph (7.8-8.2)by the way i have weekly records that i keep with the chemistry readings and i have never had a low ph reading