Did I go to far

[ohiobob]

I had a 40 gal hex tank the I had let go for to long so on Sat It was time to fix it. I removed all live rock and cleaned it,and removed all sand and left it out. Cleaned the fluval 505,and kept appox 15 gal of the old water. Put tank back together at 5pm and by 11pm both black clowns and the yellow tang were gone. That tank had been up and running for over 2 years. I guess the good news is I still have the 90 gal reef. Still bumming I lost those two clowns

 

[spanko]

Compromised your bio-filtration would be my guess. Fish died from ammonia poisoning. Do any ammonia or nitrite testing?

 

[ohiobob]

No testing done but the water did go cloudy

 

[louti]

Remember, your beneficial bacteria lives on porous surfaces (rock, sand, filter media). Like Spanko said, you killed off all of your bacteria. Also, with a water change that size, you need to mix water very thoroughly and make sure temp and salinity match exactly. Unless there is a serious issue (i.e. dangerous ammonia levels, contaminant, etc.) you should avoid large, drastic water changes like that.