I have recently lost a significant amount of lifestock and would like advice:

About my tank:
- 200 liter tank
- skimmer
- 2 filters
- 1 fan
- light unit: 1 white, 1 blue

- Quite a lot of live rock
- 2 big corals (one of which is leather mushroom) and about 10 smaller corals

- 2 hermit crabs
- 1 cleaner shrimp
- 1 pistol shrimp
- over 7 snails
- 1 big starfish, 1 small starfish

- 2 Ocellaris Clownfish (male, female)
- 1 black clownfish (female; male died due to be being stuck behind a filter)
- 4 green Chromis
- 2 Banggai Cardinalfish
- 1 Green Mandarin Goby (not sure if alive)
- 1 Red Scooter Blenny
- 1 small sized 'mystery' crab (came in with some of the life rock)

Situation:
During the holiday season we spent about 2 weeks away from the tank. We had some issues before we had a skimmer with the nitrates building up, so we left the top of the tank off. This caused a huge chunk of water to evaporate, increasing the salinity. We've had 3 casualties, but managed to improve the water after this. Since then we've had no problems with nitrates or ammonia. The PH was low, but is up to its supposed level now as well.

Since that event, we've had some (not much) dark red sediment in the front of the tank; we were told this comes from the life rock and the organisms in there dying. We have also had a returning white spot. Every time we put a new fish in, a new wave of white spot surfaces; 2 since the holidays. We have also had our Flame angel loose its colours, gain a blurry eye, a bigger white/glossy spot on its side and die as a result of that.

Other casualties:
- 1 flame angel, losing its colors, blurry eye, damaged scales on one side (slight white spot)
- 1 male black clown fish, replacing the one that died behind the filter; no apparent reason (no white spot visible either)
- 1 cleaner wrasse; lost its colours and died 2 weeks later, gasping for air (no white spot visible)
- 1 Green Mandarin Goby (not sure if alive, not seen in a while)

Because we have no problems with nitrates or ammonia or the corals, we are not sure what causes our fish to loose their colours and die.

Anyone know what this is or what to do?

Sounds like your tank is suffering the repercussions of the water getting off balance.
The water evaporation and raised salinity level more than likely caused a huge amount of stress on the fish.
There is a higher risk for death and disease when water falls out of the safe range.

The white spots and cloudy eyes indicate signs of poor water conditions, disease and/or parasitic infections. It could be one or all.
There are several conditions, diseases, and /or parasites that can cause
white spots. You can compare by following this link.

When fish are stressed a disease outbreak can occur.
Also, introducing new fish to an aquarium can introduce disease and parasites to the tank.
High levels of ammonia can also burn the thin protective layer of the eyes leaving them vulnerable to infection, which would cause them to cloud.

Acclamation is also very important when introducing new fish to an aquarium. It must be done very slowly.
The drip process is excellent way to acclimate new fish or other creatures to a tank.

Any time a fish is stressed or sick their color will fade.

The dark red sediment sounds like red marine algae also known as red slime algae. You can read more about it, what it really is, and how you can control it by following the link.



- Keep the water stable and treat for any diseases or parasites.
Then watch the tank for a few weeks before adding new fish.

- When introducing new fish to the aquarium, do so very slowly. (preferably using drip method)

- Keeping nitrates low and reduce the amount of time you have the lights on to keep red algae under control.

- Also, when keeping fish together, be sure to check if they are compatible tank mates for one another.

- Just a note, if you are keeping male/female that have paired up, it's unsafe to add another fish of the same species as they will often fight.

Also watch for aggression from male/female pairs toward other tank mates.

Good luck!

I'm hear if you have any other questions or concerns :)