24 fish and some are large tangs in a 180? are your water params top notch? zero ammo and <10-20 trates? here's a little read on ich;
The white spots that can be seen on the infected hosts are trophonts. This is the feeding and growing stage. Once it has reached maturity the trophont leaves the host. Now it is known as a tomont. The tomont becomes encysted, producing a sticky capsule. This enables it to attach to any substrate that it comes into contact with, from weeds and stones to fishing equipment, such as line and nets. Within its cyst the tomont divides many times, producing up to 3000 tomites. It is this part of the life cycle that makes treatment difficult. Since the trophont has fallen away from the fish, the fish appears to have been cured and the fish keeper stops treatment. But all the while the tomont is quietly dividing within its capsule. The tomites break out of the cyst wall and are now theronts. The theronts are heavily ciliated and actively seek out a host, without which they can survive for 2–4 days with higher temperatures lowering the time period. On finding a host the theront penetrates through the skin and develops into a trophont.
There is no dormant stage in the lifecycle. Ich does not lie in wait for a weakened fish to infect. However, any factor that reduces immunity like changes in water temperature and quality may, in a subclinically infected fish, accelerate an outbreak of Ich. The presence of ammonia, nitrite and high levels of nitrate in water does not in itself cause clinical cases of Ich. However, poor water quality will stress fish, allow an outbreak to spread rapidly and increase mortality rates in infected fish.
It has also been shown that other abiotic factors can increase both fish and tadpole susceptibility to ich. These factors include, decreased temperature, predatory cues and increased levels of UV-B radiation.