Byron i added the second filter mostly for the UV. I want those algae spores to die! All of them. A while ago i had a smaller tank(about 120L or so) that got invaded by algae. In rather short time it looked like a swamp. Green water, algae on the glass, on the snails, on the wood, plants, filter intake, gravel. It was a algae utopia. I really don`t want to remember how hard it was to get rid of them. Blackouts, dead plants, totally imbalanced water parameters, dead plants, etc. In one word(not sure i can use it) HELL.
Now algae may be a natural part of the aquarium but i think the less they are the better.
The water movement is minimum, the outtakes of the filters are positioned in such a way that they create minimal water movement, minimal enough to not be a issue.
As for the plants keeping the aquarium clean... I don't doubt they can keep it clean but they will never do what a good filtration does.
Besides what harm can 2 filters do? Except for the water movement that is minimum.
Willow thanks and yes, did try with cucumber and he just ignored it. But i will get him one day, alive and well and donate him to someone that can use his skills :).