You might want to reconsider collector for hot water use . A unglazed pool collector is designed for 15 to 20 degrees above ambient air temperature, where a flat plate collector for hot water system is designed for 25 to 125 degrees above ambient temperature. Solar water storage should be at about 140 degrees. Good luck!
Good time to take advantage of solar credits!
What he said!
Put another way: Pool heaters are not designed to run at the higher temps- without glazing they become dramatically less efficient with higher delta-Ts. They're not designed for potable water use anyway- you'd have to run with heat exchangers.
Pool heaters are great for low-temp applications, but not domestic hot water. When it's a cool-no-frigid 50F out you won't get ANYTHING out of a pool heater at 120F + DHW temps (even if you had 1000 square feet of collector- the stagnation temp at zero flow will probably barely hit 120F on 50F days), but you might still muster some 80F output for maintaining the pool. By comparison a glazed collector is still going to deliver at least some performance down to well-under freezing, and very solid performance at 50F & above. (When it's a toasty 100F outside a pool heater should will deliver pretty good 120F output though.
Glazed collectors show up on Craigslist for cheap too, but by the time you've tested & installed the system it may not be cheaper than going with a tax & utility-rebate subsidized new unit. If you're hell-bent on tinkering, wait for a glazed collector for the DHW, save the pool heaters for pools and other low temp low delta-T apps where they can run with decent efficiency. (I've seen 'em used for driveway snow-melting apps in New England, where 40-45F output on a 15-20F afternoon is good enough for the task at hand.)