Question for the experts..

[milhous3er]

A quick question about ich that have been bothering me for a good month or two.

How do we know that ich is gone from our tank ?? If we leave it fallow (or fishless) for the recommended 6-8 weeks, how do we really know the ich isn't still there. From what i've been reading, ich is always present in fish. It only shows its ugly head when the immune system is weak.

 

[pavelow360]

A quick question about ich that have been bothering me for a good month or two.

How do we know that ich is gone from our tank ?? If we leave it fallow (or fishless) for the recommended 6-8 weeks, how do we really know the ich isn't still there. From what i've been reading, ich is always present in fish. It only shows its ugly head when the immune system is weak.

I am no expert but i'll give you my .002 on the subject. I do not think there is a definate answer to your question. I will tell you that in my mind, if you follow how the ICH life cycle is explained, then yes, it should be gone once there are no hosts for them to attach to.

I quarantined a tang and then had him in my tank for a good month with 3 other healthy fish that I had for a while. He somehow got ICH, while no other fish had the infection.

I put them all in hypo salinity and the ICH appeared to go away as described by the treatment, the ICH should die in the low SG water. Then after a month in the 1.009 SG water, I slowly raised the salinity back to 1.024 or 26 and the ICH just reappeared with a vengence and due a mistake of mine, it killed the tang and one of the other fish and had infected them all. I am not sure at this time how long I left the tank without fish but it was atleast 6 weeks and I have some other fish in there and they are just fine and have been for a couple months now.

I am on the fence about ICH being ever present and being totally not there. Maybe we just do not know as much as we think about the life cycle of ICH, if it could be there at all times without a host being weak enough for it to grab hold.

 

[svejil]

Here are scientific statistics regarding fallowing a tank, and presence of ich. Please see disclaimer after statistics:

"I found that 6 weeks would give you the odds of about 99% success. That is, 1 in a 100 would still have a living Marine Ich parasite in the fishless tank.

At about 8 weeks, the odds are above 99.9% or less than 1 in a 1000 that there would be any living parasite in the fishless tank.

As far as research has found, the odds are about 100% or very close to that number, that there would be no living parasite in the fishless tank, when the tank is fishless for no less than 12 weeks.

I have heard of tanks still having parasites at or below 6 weeks, but so far have not heard of anyone having identified and confirmed living parasites in fishless tanks at 8 weeks, though there is a very small chance.

The assumptions with all this 'data' is that the tank remains active -- normal tropical temperatures, being fed, biological filter running, lighting as usual, etc." -- (Lee Birch)

Now here is the disclaimer: when folks here of reports of having a fish in QT while a tank is left fallow for however many months, then report of ich coming back with a vengence, or ich showed up again months later, it was not because ich was "ever present", but more likely that there was a "mistake" made during the fallow period. Cross contamination (siphons, test tubes, other equipment like water change buckets, etc.) can be killers in the process. A person may not even realized during a water change, or performing routine maintenace on the DT that they "messed up", but likely the protocal somewhere was not followed or lapsed. The other possibility, especially if ich doens't show up for months after the fallow period then appears, is that it was re-introduced. If you look at the scientific statistics above, even the most determined parasite 1 in 1000 in eight weeks are pretty staggering odds.

Many myths when it comes to the formidable Marine Ich, but it would appear to me if the process was followed correctly, and a tank sans host for 8 weeks, the odds would be pretty darn good.

SV