Karim - I feel for you. I am battling a similar infestation. I posted on another forum looking for advice beyond what I had already read, but the advice I got amounted to "get all the montis off the rocks, stay strong, and keep dipping every 5 days."
Here's some info from my original post if it helps...
**Disclaimer: I've read through all the threads that I could find on this topic. To summarize what I've found:
- They are persistent and hard to get rid of.
- Dips seem to kill hatched nudis, but not the eggs.
- General advice is to get montis off the rocks, closely monitor them, and dip / scrape eggs every few days (and pray that breaks the cycle).
Background:
I first noticed the problem about a month ago. They had infested the base of a spongodes colony. I took the rock that they were attached to out of the tank, completely broke the colony off the rock and threw most of the colony away. I did however cut a few frags from the tips that were far away from where the nudibranch activity was, and put those frags on a frag rack.
Since then, I found a few nudis on a pink polyp cap frag and one nudi on a Season's Greetings frag that were nearby. I dipped those frags in Tropic Marine Pro-Coral Cure, super glued any cracks between the coral and the frag plug, then moved the frags to a frag rack on the opposite end of the tank.
As a precautionary measure, I removed / dipped / glued the Undata and Stylo frags (opted to play it safe with the Stylo since their growth is similar to that of encrusting montis) that were on the same structure, but I found no evidence that the nudis had made it there yet. The only monti remaining on that rock structure is a Superman monti that the nudis seem to have been avoiding so far. I plan to break off what I can of that frag and epoxy putty over whatever I can't get off the rock.
Relevant Tank Info:
40 gal breeder, bare bottom (glass), w/ 2 MP40s for flow (so strong flow throughout the tank). The rock is landscaped into three separate structures. There are two "pillars" on opposite ends of the tank that are suspended above the tank bottom by 1-1 1/2" acrylic rods. In between the two pillars, there is a smaller "island".
There are ~12 different types of Montis in my tank. Most could still be considered frags or, at best, mini-colonies. I should also point out that I have a Six-Line Wrasse.
Currently, the only evidence I've found of nudibranch activity is on the left-side pillar. None of the rock structures touch the tank walls, so to get from one end of the tank to the other the nudis would need either 1) to crawl down the rods and scoot across the glass floor (I suspect the powerheads would blow them away) or 2) "surf" through the tank and hope they land somewhere on the other side.
On the other end of the tank, I have a few more montis, but the main one I am concerned about is a Leng Sy colony (~7 in across). I can see underneath the colony pretty well, and I haven't seen any evidence that the nudis have made it over there.
