the reason i said 50% is because this allow the owner o do absolutely nothing else, with no other equipment. no dosing ca or carbonate. phosphates and nitrates would surely stay low, unless the owner feeds like a madman. this type of system would make more sense the smaller you go, i want to set up a 30 gallon cube this way, water chnge vessel and pump underneath...not a sump.
and to answer your question i don't think what you are describing is possible, if it was you'd have to have a very low bioload to gallons ratio and a very high algea to bio-load ratio, probably by way of an algal truf scrubber, but then yu just added a filtration device that takes upkeep and power, water changes could be easier and chaeper depending on the size of the system.
i don't think chaeto floating in a sump is nearly as effective as some think. personally i feel its main benefit is pod production/habitat.