[quote=omard;396560]What keeps them from spreading from refugium to main tank? --- Seems like they would in time.
My refugium is set up apart and separate from the sump.. Another reason they should not be one in side the other..
I have my fuge set up with the feed /supply from main pump and then on the outlet from fuge to sump . I drilled the Bulkhead about 3 inches under the top rim of the 20.High then I added a 1 in 90. then a stub just tall enough to set at finale fuge water level.
That stub is drilled with 1/8 th in. bit to look like a sieve and thats the main drain strainer then the top of that I. inch stud serves as a overflow drain in-case I ever forget to wipe that drilled stub out every week or so. But I have never had them in my main tank. And the flow rate through the refugium is less then 20 GPH so nothing much could really push them through.