Things are coming along nicely. I have heard that mangroves are super slow growers so it might take them a lot longer before you see any change. One thing too is if the potho's is planted in the HOB their extensive root system can get huge and creep into the motor. I kept my potho's just hanging in the tank.
I'm surprised they are catching detris in the water flow. Don't let it build up too thick and if it does take them out and rinse them off.
I'm not sure they "fully bloom" like you're expecting them to. Corymbosa a flowers stay pretty small and don't open up like normal garden flowers. Here's mine, been flowering for a couple months now. Yours does look great though, glad its working out for you
That is so cool! I love when plants flower.