The lifecycle of Marine Ich can vary based on a number of factors - temperature, salinity, fish species, etc. For that reason (and likely others), the TTM process was designed to be pessimistic about the timelines. Trophonts may have a timeline of 3-7 days in 80F water, but at 75F (perhaps even 78F) this may extend. By running the TTM process for an extra cycle, you are more likely to ensure that the fish is actually ich-free.
In the end, it's a matter of your own level of risk acceptance. The Trophont stage is known to last as short as 3 days, so wouldn't two transfers over 4 days potentially be enough? Perhaps - but there's a risk of it not being enough as well. That's the idea behind the "extra" transfer.
In the end, it's a matter of your own level of risk acceptance. The Trophont stage is known to last as short as 3 days, so wouldn't two transfers over 4 days potentially be enough? Perhaps - but there's a risk of it not being enough as well. That's the idea behind the "extra" transfer.