Originally posted by Bomber
Just on ick. Trophonts do play the drop and sit routine. However, theronts are conditioned to hatching a few hours before first light. That greatly increases their chances of if not re-infecting the same host, finding another host that has taken up the same home for the night. They are oriented to traveling up, off the bottom (they are not oriented to substrate, that would lessen their chances of survival), which again increases their chances of finding a host. It also increases their chances of being up and in the water column to be picked up by a UV.
As most fish in an aquarium hole up in the same place every night, there is a very good chance they will be reinfected with the offspring of the parasites that detached from them, for the very reasons you describe. Due to the proximity of the fish to the substrate, the theronts have a much greater chance of finding the fish before they go anywhere near the sterilizer.
If you understand how they work, it's obvious why a UV is very effective against them.
I understand the life cycle of "Ich" only too well which is why it is obvious to me that UV is not very effective against these parasites.
There are several other reasons for hobbyists using a UV too.
One, most hobbyists cannot distinguish between Ick, Velvet, Brooke, etc. UV will treat them all.
Brooklynella has no free living stage. As the parasites do not need to leave the fish to reproduce, UV is going to be completely useless in saving an infected fish. Further, as parasites can pass from fish to fish that are in close proximity, it will also be able to infect other fish without going anywhere near the sterilizer.
Two, UV will work in a reef tank with corals and invertebrates. Nothing else will.
Prevention works great for a reef tank with corals and invertebrates.
Three, if you understand what UV does, not just biologically but chemically in saltwater, it's a win win for reef tanks.
Please explain what this comment means.
The problem with UV is even if it was tuned the best way it could possibly be tuned, parasites can still survive in the tank without passing through the unit. There is no way you can guarantee that all parasites will be eliminated. If all the parasites can't be eliminated, at best all the sterilizer will do is reduce the numbers of parasites. This means you have to keep running it continuously and if you turn it off, you risk having the numbers of parasites bounce back to dangerous levels.
Tuning also means having the circulation in the tank configured in such a way that there are no dead zones and flow in every part of the aquarium will force all water and swimming parasites towards the inlet of the UV sterilizer. This is a very difficult thing to do and is virtually impossible to validate. So even if you have all the best intentions, you can't guarantee it will be even partially successful.