You got me thinking about flow, and sure enough a classic mistake. Canister filters overdue for maintenance, flow rate slowed way down. Cleaned the big canister tonight and ordering more filter pads so can do the other two soon. The two smaller ones I had connected together to share an intake/return, but split them again so they're both running, giving more them each their own spray bars. This adds more flow through each bar, and I adjusted some spray across the top and some spray down into the water too. Can see the plants waving in the flow again -- should have been obvious. Thanks again, this and some good siphoning should start clearing it up.