Is this a correct assumption


New member
If my reef tank has not had any disease outbreak for the last year, and I add a blue tang that has been properly quarantined to it, and I do not add anything else to the tank before quarantining it, my new tang will never get Ich (even though they are susceptible to it) ?

Alternatively, if I add anything to the tank without QT and after 45 days the fish do not get Ich, does this also mean that they will never get Ich - assuming no more additions are made?

was that clearly stated? :rolleyes:



New member
It's as clear as fog. :D Joking!

That first paragraph has quite a few assumptions attached to it. Mostly, you have covered the assumptions generally, but not specific enough for my way of thinking. The concept of quarantining a marine specimen does not mean it is free of disease. What you want to be clear about is that you are talking about disease-free; possibility of being diseased; or known to be diseased. So my changes would be this:

1) If my display tank has no disease in it after a year. . .
You see, a tank can be diseased without you knowing it. It can get a disease by adding something to it that was not free of disease (see below);
2) and I add a blue tang that is disease-free. . .You see, quarantine doesn't mean it's disease free. Quarantine is a means to verify the fish is disease-free;
3) and I only add things to my tank that I know to be disease-free. . .See 2)
4) then my new tang will never get Marine Ich if I keep my display disease-free.

I hope the above subtleties are clear, as to how they differ from what you proposed. How do you guarantee disease-free? Quarantine is a means to do that, but like I wrote above, the act of quarantine itself doesn't mean the specimen(s) is disease-free. You see, I don't assume that 'properly quarantined' means the specimen is disease-free.

As to your next paragraph. . .
1) If I add a possibly diseased marine specimen or possibly allow the disease to enter my disease-free tank by some others means. . .
2) and the display does not come down with a disease in 45 days. . .
3) then there is no disease in the display. . .
4) assuming I do not add any disease for sure during that time?

Answer: Probably. With a UV maxed out for killing Marine Ich (MI) and other control features in place, the disease can still live, but not express itself in large enough numbers for the aquarist to actually see it. So under the carefully worded conditions above (my changes) a 'regular display tank' (i.e., one without MI controls) would still be disease-free.

Hope this clear? :rollface:


New member
LOL I forgot what I was trying to say.

What I am trying to prove or disprove (actually better understand) is: "Ich is (or is not) always present in a reef aquarium"

If Ich has a life cycle of 4 weeks and needs a fish host -then without a fish host the next generation of Ich would not survive.

So if a tang placed in QT did not show the visible signs of adult cryptocrayon, then once it is placed in an established "disease free aquarium" there would be no way of any of the fish in that aquarium to get Ich.

I also say "disease free aquarium" because if the fish have been visibly disease free for a year, then none of the fish dependent parasites could survive without making their mark on the fish.

On the otherhand, if what you are saying is correct; then a QT tank without a UV sterlizer will not guarntee a disease free enviorment - once the fish is placed back into the "disease free aquarium"

Am I adding more smoke to the fog ? :)


New member
That's easy. That's an 'old question.' Marine Ich (Cryptocaryon irritans) is only present if you let it into your tank. That's all there is to it. :D

The "life cycle" set at 4 weeks is a problem. Science and Nature likes ranges. Marine Ich (MI) has high and lows. The 4 weeks is only an average. As you increase time, you decrease the likelihood of the disease being around. If you choose 8 weeks, then you have about a 99.99% chance that all the MI is dead.

BUZZZZ! Wrong answer!
Seeing is not believing. Here we go again.
MI can reside in the gills -- out of sight of the aquarist. In fact the gill is the most likely place to find MI. Why? Because fish 'breath' by passing water past the gills and when that water contains the infectious MI phase, then there is a greater likelihood that the MI will get to the gills before it gets to the body/fins.

NEXT: What you see as a white spot is actually only the end of the MI phase. This is when the MI is 'pregnant' and ready to drop off. When the MI is just burrowing into your fish, and before it becomes engorged, you can't' see it at all with the naked eye.

The above are the reasons why I changed your text to actually know whether or not the fish is diseased NOT whether or not you can see it.

Regarding: I also say "disease free aquarium" because if the fish have been visibly disease free for a year, then none of the fish dependent parasites could survive without making their mark on the fish. You are missing another fact. :D

When no new MI is introduced into a tank, the MI already there go through multiple generations. It turns out that after about 10 months, (15 or so generations) that the MI is too weak to infect fish. So, your "year" would be beyond the ability of the old MI to do any damage.

Your last paragraph doesn't fit what I meant to say. Maybe it is not clear. I'll take a slap for this one! :eek:

I was not meaning the QT had to have UV. UV is a control, not a killer or cure for MI. MI can live and re-produce in your display and still be kept under control from large blooms of infecting free-swimming MI by the use of strong currents, UV, ozone, and other 'things' which inhibit or 'control' the MI from becoming a massive outbreak.

Any better now? :rollface: