Big trouble

I did a water change 2 days ago and the next day my mandarin fish and my yellow taile damsel had almost turned white my clown fish has brown marks all over its body my corals had all colapsed. I run my water thorough a reverse osmosis unit but I think something might have got past this. do these units clear out chlorine from the water? I had half a bottle of water safe so I just thought this is a make or break scenario here i just poured the rest of the bottle in and an hour later all the fish had started to change back to normal and all my corals are fine now.
I am now wondering if I should add tank safe to any water that I add to my tank even tough I run it through the Reverse osmosis unit.
Any one else had this problem?
All advise welcome as I have only had this set up since November

30 Gallon cube tank
30 lbs live rock
1 yellow tail damsel
1 mandarin
1 bi coloured angel
2 clown fish
1 Royal Gramma
3 red legged crabs
1 boxer crab
1 cleaner shrimp
3 turbo snails
9 various corals
1 anenomie.

 

I did not check the alkalinity but the PH and temp were fine

 

Did you use a hydrometer or refractometer that has been recently calibrated to check your water change water? I would doublecheck your salinity with a calibrated instrument.
Also, RODI should remove everything from water, I believe except Chloramines. Do you have a TDS meter to check the output of your RODI unit? Was the RODI unit new when you got it, in November? When was the last time you changed your filters in the RODI if not? You shouldn't have to use any additives if you have a well maintained RODI unit.

Also, did you checked your other parameters, ammonia, nitrate, nitrate? You have a lot of fish for a 30 in my opinion and not a lot of rock. Keep an eye on your ammonia etc.

Did you aerate your water change water? With that many fish in there if you added unaerated water you could potentially have removed a lot of oxygen from the water and whatever was left may have gotten sucked up quick by all the fish.

Just some ideas, good luck.

 

how old is your tank?

 

Too many fish and not enough live rock is your problem

 

My Tank is 5 months old.
The RODI unit is 4 months old this problem has only happened the once I normally change about 4.5 galls of water every 2 weeks this time i had changed 10 gallons. I did not aerate the water.Nitrite and amonia are fine nitrate is a bit on the high side that is why I gave it a larger water change.Sorry I have made a mistake it has 30 lbs of live rock not 15

 

To keep the new water close to the temp of the tank, I bought a cheap heater that I put in the RO/DI water. It assures me that it is the right temperature. They also sell a TDS meter cheap. I got one for about 20 bucks online. This will assure you if your RO/DI unit is actually putting out 0ppm.