The one problem I see is the piers holding up the grow beds. Once you ad your media and water, you may need some additional piers under the middle. Also, you overhang over (I guess it's the in-ground fish tank) may be a bit too long because of the weight and not enough support. You are talking about a considerable amount of weight with media and water. As for media, red lava rock is light and excellent for grow beds.

Also, be sure to level and re-level with shims length ways and cross ways about ever 1 to 2 feet or you will wind up with puddling in your grow beds.

Additionally what are your Bluegill use to for food...live or pellet. If it is live food you could run into the same problem our member WATERBOY has Crappie are picky eaters!!

Keep the pictures and up dates coming.

Also go to your profile and put in where you are located. There may be other members close by who might want to lend a hand.

Good Luck