When looking at solar panel designs it is all a matter of trade offs, ground mounting in prepared bed is an option if you have enough room, this usually means preparing a smooth ground surface, spreading plastic ground cloth and a layer of smooth gravel to keep plants (roots, etc.) from trying to grow into the panels and just lay them out on the ground. The trade off here is that you may be far away from the optimal mounting angle for your latitude. See this web site
Optimum Tilt of Solar Panels often people make the mistake of mounting pool solar panels at the optimal year round angle for PV solar electric panels, but the demands of pool heating are different. Depending on your region you may want to mount at either optimal summer angle, or optimal spring fall angle, or somewhere in between. This will depend on the expected length of your extended swim season. You appear to be at 40 degrees north, so your optimal summer angle is 12 degrees from pointing vertical, and your spring/fall optimal is 37 degrees (Optimal summer angle would run from April 18-Aug 24th) Which is close to the typical swim season for much of your latitude, so if you are just wanting to boost your summer pool temperatures, sticking with something around 12 degrees from vertical, but if you are wanting to extend your season much beyond those dates you should plan to tilt closer to the spring / fall 37 degrees which are optimal starting on march 5 - October 7th. Of course extending your season will require more panels and just boosting summer time peak, as the available amount of heat from the sun in the spring and fall is much lower due to the lower peak solar angle. The kicker is all of this much be weighed against the relative cost of the panels, the cost of the mounting platform, and the available space to mount panels. If you have the available space it may be worth it to just ground mount more panels vs building expensive racks to tilt them to optimal angles.
Having said all that installing over brick may add some benefit, but the brick should be mostly protected from solar heating during the day by the panels, so you may not get as much gain as you would like. Remember a solar panel with optimal flow through it should be relatively cool to the touch when operating (a couple of degrees above pool temperature)
Ike