At my old house I created and maintained a 300 gallon naturalistic pond that included fish, many plants, a section at one end that acted as a biofilter (lots of water hyacinths and iris) and a pump that took that water to the other end which had a waterfall. I changed about 10-20% of the water maybe 2x/month and cleaned out the filter occasionally. The water quality was great for years.
At a new house now and have this concrete water feature, 7.5' x 3.5' x 1.25', ~200 gallons. There is a screen about 10" from the top on the water that holds the rocks, then an additional 6-7" below that which holds an Aquascape Ultra 800 pump (790 gph with no rise). This is set in the center bottom, pushing the water through to the top surface, disturbing it enough to stop mosquitoes. The water is being pulled through an Aquascape filter that is set to one side. My plan this year is to let water lettuce populate the surface and see how the water quality is. Maybe in the future there will be a single (small) hardy water lily, lotus or other similar plant. There are no fish and will never be any. The feature was filled 48 hours ago and is in full sun from 7:30 - 4:00.
I know from experience that I want some of the surface covered to help with algae, that the algae that forms on the sides and bottom is beneficial, and that as many plants as possible to suck up nutrients is good. But I've also had a fish load in the past to deal with and here I won't.
My first question: the filter is off to the left and is shooting up through the center. Is this enough water circulation or should I add a t-connector so that the water circulates to the other side as well as straight up? There's plenty of power in the pump to do this. I currently have the valve on the output turned down a bit so that the water doesn't shoot out the surface quite so forcefully.
Then in terms of plants, coverage: the water lettuce is already doing well and will populate well. Do I need plants like Anacharis in this setting like I did before to balance oxygen and nutrients? Or is a floater like the water lettuce fine? Thanks!