We are opening our pool for the first time and need some guidance as to the best place to purchase supplies for the season (we live in upstate NY). We are aware of "InTheSwim" but that's it. Any guidance is helpful.

intheswim.com
WaterWarehouse.com
Leslie's Swimming Pool Supplies

I believe all have coupons. Sign up for all their newsletters too as they may send coupons that way.

Some have free shipping / free next day delivery too.

Get on Leslie's Mailing list and watch their sales. We find shock in the craziest places cheap... Valu Home Centers for one. What kind of system are you using? Also, if you look at your local pool centers compare prices. One place will have XX for less, another will have XX for less. If you are willing to run around you can save some cash that way.

Since it is your first time opening, spend some time at gardenweb's pool and spa forum . Those people are experts and willing to help a newbie.

I'm interested in the OP's question as well. Thanks AMS for the useful feedback.