I'm sure you have done much reading and research, but just wanted to share another concept. http://www.angelfire.com/ab/rayjay/fry.html

And in regards to your roti culture, the 53 sieve is clogged. Either from a dense culture, ditritus, and or an unclean sieve. Try screening a smaller amount of water. Be careful not to disturb the culture before screening so you don't pick up extra the ditritus.

How green is the fry water? If you want it green, the skimmer would skim all that out.