<a href=showthread.php?s=&postid=15292921#post15292921 target=_blank>Originally posted</a> by evsalty
Looks like we can rule out the sandbed removal as the cause.
Something did though cause you to have the algae issues.
Did you ever test for phosphates?
How old are the bulbs?
Was your nitrate reading of <10 taken while you had the nussaince algae all over the tank? I ask this because large amounts of nussaince and good macro algae will usually give you a 0 reading even though the algae itself is holding high amounts of nitrate.
Quite a large proportion of aquarists using GFO in reef aquaria have reported undesirable effects on corals. These reported effects include tissue recession and bleaching. Many advanced aquarists have associated these effects with the first addition, or with a later change, of the GFO.
<a href=showthread.php?s=&postid=15293245#post15293245 target=_blank>Originally posted</a> by cabrego
I think everything has been covered excpet for your actually water source,
I assume you are using RO/DI,
When was the last time you checked TDS?
have you tested for copper?
<a href=showthread.php?s=&postid=15293246#post15293246 target=_blank>Originally posted</a> by wrott
It's odd that the fish died before you removed the sand.
This would suggest something very out of wack, like sand bed crashed or some other contamination.
Did the sand look black anywhere, hydrogen sulfide?
And the huge algae, diatom bloom also suggests a large amount of nutrients were added somehow.
So you have only 2 fish remaining now, it is baffling. I hope the problem can be answered, as it is a devastating event that I know you want to avoid in the future.