Regarding the gravel for the BG. You can put the pea gravel where you think is best, but the BG might not agree. It's hard to determine where the BG will spawn, until you observe them spawning in your pond. I've made areas for them and they've ignored those areas, just to use them 2-3 years down the road.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).