I was getting some staining recently and consulted Howard Bond who is a master photographer and printer, and teacher. Occasionally my toner batch would go bad with floating debris and a ugly color, but no white growth. His technique is to mix Kodak Rapid Selenium toner with wash aid. Liquid fixer is mixed without hardener. Prints are stored in water during the session without proper washing. Prints are taken from the water storage tray directly into the toner, then treated with wash aid, then properly washed. Periodically black precipitate in the bottom of the toner bottle is removed from the mixture, and fresh toner is added to recharge the strength of the toner. The toner is apparently used for quite some time. I have been using this system for 2-3 months with success. However, the number of prints that I tone is rather insignificant. He advises me that the wash aid mixed with the toner provides a proper ph level to avoid staining. It may also avoid bacteria growth, not sure.
I do something similar to this. I never store selenium toner because I would spend more time cleaning all of the stains and filtering the solution than I would spend toning prints.
I process prints in the normal sequence with 2 fixing baths and no hardener. Then PermaWash and a regular wash. For toning, I wait until I have a volume of processed, dried prints, say 20-50. Then I mix KRST with Permawash for the toning mixture. I soak the dried prints in Permawash, then tone with the KRST + Permawash solution. Usually I do that in batches of up to 8 11x14 inch prints at a time, interleaving them like processing sheet film in trays. If I use concentrated toner I do just a few sheets at one time so that the toning color does not get away from me. Then I rinse the toned prints in fresh water before transferring to the archival washer. No staining problems and much more time efficient than I used to be.
Also, I use single tray processing. The Permawash and the KRST + Permawash solutions are stored in 5000 ml plastic beakers. I pour the Permawash into the tray, then put in the prints one at a time so they don't stick to one another. I use disposable latex gloves and then rotate the prints, interleaving them in the tray. I use a tray one size larger than the paper. When the time is up, I dip my wet hands in a small bucket of clean water to wash off the gloves, lift the tray to pour the Permwash back into the beaker, and then pour in the KRST+Permawash solution and repeat the procedure. This greatly reduces selenium stain in the tray and in the beaker. Also reduces the amonium smell because the toner spends most of the time in a beaker rather than a large open tray. Also reduces handling of prints with tongs. Whenever I used tongs I would mar the emulsion somehow, even being very careful.