Non CO2 methods easily go 6-12 months without any water changes and those are only done to remove detritus and mulm build up after pruning.
Rather than water changes for export, you trim the weeds for the nutrient export.
You can add less light, say 1.5 to 2w/gal (at most), this will reduce the need for water changes and CO2 also.
Some of the plants will not do so well, but most of them will in your set up.
You will need to add water for evaporation.
You can check my site on the free side for the non CO2 methods, it will give you more info.