please help revive my tank

[toolie]

9 months ago i moved house. when i moved into the new house i noticed my fish started dying. i lost a clown, a lipstick tang and a dwarf lion fish. i didn't notice the lion fish had died in amongst the other slowly dying fish. I pulled the bodies of the clown and lipstick tang but was unable to find the body of the lion fish. my tank and sump is 620L total volume with a plentium sand bed.
I have been trying to recover the tank with water changes and siphon the green hair algae and gray cloudy substance in the sand and on the rocks.

This all happened because i lost the will to keep the tank going, (once all my fish had died.)
Six weeks ago i started water changes "big water changes" 200lt at a time every 2 weeks added 30 snails, carbon and increased water circulation by 40%.
My questions are: Is my plentium toxic? How can i get rid of this gray cloudy substance and Green hair algae? or do i have to start again?

1 red sea skimmer with 7500lt pump
2 1x chiller
3 2x 10000k 150watt MH lighting
4 1x 5000lt return pump
5 2x 4000lt circulation pumps
6 100kg live (i hope) rock
7 5x corals i want to save from my negligence.

 

[Scooterman]

Sounds like when you did the move you didn't tear down the plenum, at that point while moving I would of taken it down & cleaned it because moving will stir up things too much. I would suggest @ this point tearing it down & cleaning it throughly, get it right & it should last you a long time, as long as you don't move again

 

[toolie]

You are correct Scooterman... I built the stand so i could pick up the tank with the sand bed intact.

 

[Scooterman]

That would sound about right then, I would clean it, I would probably replace the sand also, sounds harsh but my best bet from what your telling me.

 

[toolie]

Replace the sand... Big costly job.
I tested the water and the water is as follows:
ALK: High
PH: 8.2
AMMONIA: 0
NITRATE: 0 (surprisingly)
NITRITE: 0

But these readings may be due to the large water change.

 

[theJ]

toolie, how deep is your sand bed, how old is the tank?

 

[toolie]

Sand bed is about 6cm deep in total, course rubble with a layer of fly mesh and very fine coral sand.

 

[toolie]

Sorry how old is the tank?
before the move my tank has been running for around 1 1/2 years

 

[toolie]

Having a look through the old photos. This is what it looked like before the move.

 

[toolie]

Now after...

 

[hdben]

After doing a water change scrub the rocks off to remove hair algae (in old tank water). Even if your water reads ok I would bet the hair algae is holding all the nutrients. Giving them something to feed off while your changing the water trying to export residuals. JMHO, good luck.

 

[toolie]

Thats a good idea to scrub the rocks before a water change.
Do you think my sand bed needs to be deeper? I can clean the old sand and add more so the new sand will seed quicker.