Marine "Ich"
Marine "Ich" or "White Spot" is probably the most frequent fish disorder encountered by aquarists keeping tropical marine fish. It is also probably the disorder that is most misunderstood by aquarists. However, because this disorder is also encountered in aquaculture, substantial research has been undertaken and the picture is somewhat clearer than many believe.
What causes marine "Ich"?
Marine "Ich" is caused by a ciliated protozoan called Cryptocaryon irritans Brown 1951. Ciliates (Phylum Ciliophora) are one of the largest groups of protozoans and all posses cilia or compound ciliary structures for food acquisition or locomotion at some point in their life cycle. Of the some 7200 species that have been described, around one third are ecto- and endo- commensals and parasites C. irritans is an obligate ectoparasite (****erson and Clark, 1996) which means that it is an external parasite that needs the fish host to complete its life cycle. The name 'Marine "Ich"' has been coined because it is essentially the marine equivalent on Ichthyophthirius multifiliis Fouquet, 1876, or "Ich" for short. While the two species of ciliates have superficially similar life cycles and signs, they have been found to be only distantly related (Wright and Colorni, 2002) .
The life cycle of C. irritans
The life cycle stages of C. irritans
C. irritans has a four stage life cycle, as shown in Figure 1. The parasitic stage (trophonts) is the one that results in the appearance of white spots all over the fish. The trophonts burrow under the skin where they feed on body fluids and tissue debris. When the trophonts first infect the fish they are small but grow as they feed and so the white spots are initially small but get larger as they mature. Once mature, they drop off the fish and sink/swim down to the substrate where they encyst and begin to reproduce. In this stage they are called tomonts. After a number of days in which the tomonts divide, the cyst ruptures, releasing the tomites. Tomites may differentiate into theronts, the infective stage, which actively seek a host to reinfect.
Figure 1: The life cycle of C. irritans (After Colorni, 1987).
When the theronts (parasitic stage) are embedded in the skin of the fish, the fish secrete a thick layer of mucus in response to the irritation and they are protected from outside influences. This makes treatment of infected fish difficult.
The timings of the stages of C. irritans
lengths of each of the stages of C. irritans as determined by various authors and studies. Despite each of the authors working in different locations and having different sources for the parasites, the findings are consistent. Trophonts will attach to the fish for at least 3 days (78 hours) and as long as 7 days at around 25°C. When the trophonts drop off the fish, they can take as little as 30 minutes and up to 24 hours to reach the substrate, with the majority encysting towards the shorter end of the range. The reproductive stage appears to be quite variable. Reproduction can be complete in as little as 84 hours (3 days) but can extend to as long as 12 days and even longer.
i just got this off google dude hope this helps | 
.... imo do a water change and see if it helps . what are you dosing for??what disease ? 
