Has ‘Fallow period’ started if there is still fish in tank?
Good point. From Humblefish's post on another site:
The reason to go fallow (fishless) is to eliminate a fish disease from your DT (display tank). Going fallow works because you are denying the disease a fish host to feed on, essentially starving it to death.
In order to go fallow you must remove ALL fish from your DT. If just one fish is left behind, even a “disease resistant” species, then going fallow is for naught because the disease will continue its life cycle. Corals/inverts can be left in the DT, as those are not capable of hosting - although some are capable of “housing” the encysted stage of certain parasites for a period of time (see “Fallow Periods” below). It is important to continue to feed your corals/inverts while going fallow, and also put a pinch of flake or pellet food into the DT every 2-3 days to feed nitrifying bacteria in the absence of fish poop. Continue to do everything normally with your tank while going fallow; although you may wish to go lights out if you are running a fish only system (just don’t forget to feed that bacteria!)
Fallow Periods - Below is the general consensus fallow periods for all diseases that require it. In most cases, it is the longest known time period that the encysted stage can survive on corals, inverts, rocks, substrate without a fish host to feed on. The fallow period starts when the last fish is removed from the tank.
Black ich (turbellarian worms) - 4 weeks
Brooklynella aka “Clownfish disease” or “Brook” - 6 weeks
Flukes (monogenean worms) - 4 weeks
Ich (Cryptocaryon irritans) - 76 days
Uronema marinum - No fallow period, as it does not require a fish host to survive. It is an opportunistic parasite that strikes when a fish’s immune system has been compromised. Uronema mainly affects damsels (especially chromis) and clownfish.
Velvet (Amyloodinium) - 6 weeks
During the fallow period, the fish must be quarantined and treated for whatever disease(s) are afflicting them. Successful treatment is imperative to avoid disease(s) from being reintroduced into the DT.
Quarantining all future livestock purchases is also very important to avoid having to go fallow again in the future.
After the fallow period has ended, you can return your fish to the DT. I recommend doing it one fish at a time, spread out over a couple of weeks. This will give your bacterial levels time to adjust to the added fish bio-load, and avoid a potential mini-cycle/ammonia spike. I also prefer to add back smaller fish first, so they are established ahead of the larger, more aggressive ones.
