There will always be conflicting opinions and advice on this topic.
First there is the never resolving issue of two camps, eradicators and managers. Which approach one subscribes to dictates everything else about how treatment and intervention should be understood. For example, if you manage ick, then a QT is only a place to let a stressed fish calm down, or may be to get some medication for a secondary infection. If you are going with eradication, then there are specific and strict protocols to follow depending on what treatment approach you chose (hypo, copper, or TTM).
Now for purposes of this thread discussing fallow periods in the display only apply if you are trying to eradicate. If you are living with/managing ick, then the fallow period is pretty pointless in the first place.
So let's assume we are talking about eradication plans. Here the fallow period discussion also allows for a lot of varying opinions and perceptions. Ick has a well understood basic life cycle, but there are also some variables. For example the number of days it takes to complete the life cycle; derived from statistics. (I'm making up numbers here for the purposes of discussion and to illustrate a point with out having to dig up the books...) If one stage lasts 2-3 days as we know it, then really it's more like 98.8% completes that life state within 2-3 days, and 99.4% complete that life stage within 2-3.25 days. Bla, bla, bla...... Same thing with fallow time. We know that under normal circumstances 6-8 weeks Should be adequate for all ick to die out. Well in reality that means that probably 99.? % will have died out within 8 weeks, leaving some slight chance that a few will survive a little bit longer. Add to that, theories have evolved about different ick strains that may have somewhat longer life stages, AND theories that sometimes ick may have some ability to lie dormant for longer, and it gets a lot less clear.
So what is the right fallow time? (again, Making up numbers to illustrate the point)
6-8 weeks = 95 + % likelyhood of eradication
10 weeks = 98% likelyhood of eradication
12 weeks = 99.5% likelyhood of eradication
Just like the birth control pill, it's about percentages. 6-8 weeks is more often than not effective. 12 weeks is much more consistently effective. There is no absolutely assured 100% answer.
