Fish problems

Swollen Bellies
l sometimes encounter calls from customers telling me their fish have very large bellies (common to Triggerfish and other big eaters). Are you feeding your fish those small, pink, salad shrimp? Those are not raw and have little or no nutritional value. They can also constipate your fish. Try feeding the more seaweed or Nori. Hopefully things will pass. Mixing an antibiotic such as erythromycin or kanamycin with their food will cure any bacterial infections if that is the cause. Once they stop eating there is nothing you can do but wait.

Toxic Shock
Please be careful when adding new livestock to your tank, especially sea apples, medusa worms.
If you add new stuff to your tank and fish go to the bottom, breath heavily and/or die, toxins may have been released from new inhabitants because of stress. Some of these toxins are extremely strong and act very quickly. If your are faced with this dilemma, CHANGE A LOT OF WATER IMMEDIATELY. Also run a small amount of carbon for 2-3 hours flipping the bag to expose all of the carbon to water. Water passing through carbon is much better than passing over it.
Replace carbon with a new batch and change it after 8-12 hours. This should solve the problem but repeat if necessary.
To avoid this problem, acclimate cucumbers, etc. as described in SeaHorse Tips
Avoid sea apples and medusa worms all together.
The thought that leather corals should all be kept at the end of your tank where the overflow is to prevent them from poisoning other corals is ridiculous if you have any circulation in the tank. Any "toxic" effect will be spread dozens of times faster by internal pumps than it will be removed to your filter below. This also implies you cannot keep leathers unless you have a sump type filter - not true.