what r possible reasons for my corals to die?

[mr.clownfish]

my xenia, clover polyps, and my brown toadstool leather just died. my frogswan, hammer, bubble, zoos, mushrooms, yellow toadstool leather, and colt coral are all fine. i dont have a clue what happened... but before they died i had a lot red algae that just appeared.
now i have to admit i did something very wrong that could have been the reason y they all died

my sand was very dirty and had a lot of junk all around, it was really ugly and i just removed a lot by using a long plastic tube. so in like a week it would all come back.
so i took all the rock and corals and everything out even the water and i took the sand to the backyard and washed all the dirt out with the garden hose. there was A LOT of junk that came out and my sand was sparkling. i drained all the water out and i refilled my tank with the same water i was using before and same rock and same corals same fish everything was the same only it was cleaner.
could the problem be from the hose water??

after that i got a lot of red algae my brow toad stool was just covered by it. my polyps died then got covered, and my xenia just fell apart.

 

[spiderwoman]

What are you water paramaters. That is you need to test first and start the debugging. My guess is that you have high nitrates and/or ammonia. I'd recommend either getting a RO unit or get RO water for your salt mixes and top-off.
Also when you hosed your sand down, you killed all of your biological filtration that had developed in the sand.

 

[calvertbill]

RO/DI water heads off so many problems before they get started.
Test your water for everything. I would suspect high nitrates or phosphates, or both. Leathers are usually hard to kill (I once harvested four out of *****'s garbage pail) so I'm pretty sure you've got a water quality problem.
We don't have a lot of details to go on, though. The rules are basically the same:
1. Highest Water Quality
2. Appropriate amount of light
2. Appropriate amount of flow
P.S. I hope you didn't wash your LR!
You might want to board your remaining corals until you jump start your biofilter.