Starting over on an established tank

[crownvic4life]

I have kind of a weird question/situation. I work at a small zoo and we have 1 125 gallon saltwater tank and 1 75 gallon. The 75 was empty when I started so I have cycled the tank and have since added fish and it is flourishing. But, the 125 gallon was poorly thought out by my predecessors. The rock was just haphazardly thrown in and the fish are burrowing under and compromising the integrity and the rock is collapsing. They also installed new lights and the feeding schedule was a little excessive, combined with insufficient water changes led to a horrific outbreak of hair algae. There is also a pretty bad case of aiptasia. I have made significant progress on the hair algae and have been working at the aiptasia. Id like to set up some temporary tanks for the fish and re-do the rock work and add some new live rock. I know that the tank will need to cycle again, but can I keep the sand?

If I do peroxide on the rocks (there are no corals) I know it will likely kill the good bacteria I had going in there but at this point the falling rocks are a hazard to the fish and glass tank. Does anyone have any suggestions, tips? Should I essentially just treat this tank like a brand new one?

I did not stock this tank and we don't have a lfs anywhere near me but here is the livestock in the tank. 2 Ocellaris, 3 convict blenny, 1 lawnmower, 1 powderblue, 1 picasso trigger (I know should not be in this tank but I don't have a lot of options for it). Again I did NOT stock this tank, the person before me did and didn't do much research they just made a "nemo tank" all seem to get along and are at least 2 years old.

Any help or input will be greatly appreciated!

*editing for filtration-There is an under tank sump/refugium (not exactly sure the size on it) running over filter floss and bio balls. There is also a skimmer, here is the link for the one we have Im pretty sure
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4392+23953&pcatid=23953

 

[Sk8r]

Easy peasy. Remove fish to safety, then remove rock and sand. WASH the sand in ordinary tapwater, and wash it until water runs clear. FInish off with Prime (dechlorinator-conditioner) on each batch of sand and drain. That renders the sand full of demised bacteria, but no actual detritus. The rock is a different story. Rinse it off in the cleanest of the salt water you extracted from the tank and do NOT rinse it in tapwater. Place it in salt water while you clean up the tank and set up.
White vinegar will clean all the white crust off everything, including glass.
Reassemble the tank with a better job of stacking the rock, using superglue to cement the very small rocks into somewhat nicer pieces, but NOT gluing it into massive heavy bits which would make adjustment a pita.
Personally, I underlay the rock by putting eggcrate lighting grid (the white stuff) on the bottom of the tank (I install nassarius and fighting conches, which can clean undersand areas and which will clean the little squares. Plus a lot of bristleworms.) This means that your rock stack will stay put and not roll down.
Replace your now-washed sand into the tank AFTER the rock goes in, add new salt water, and expect that the tank will cycle in about 5 days, maybe a little longer. Give it a little pinch of fish food daily, and just test daily, looking for your ammonia spike. If you don't get a definite one by 7 days, figure it was just a very small one and proceed gingerly.
At that point, start putting the inverts and corals in, and add the fish in one or so at a time, separated by days, to prevent too heavy a load hitting the sandbed, where the bacteria will be breeding and getting up to strength.
The fact that the rock's processing power is still intact all the way to the core of the rocks means that you will not have a long cycle at all.

I'd also shake the filter floss in favor of a filter sock often cleaned; and get rid of the bioballs, 3 at a time if you are getting rid of them on a tank with live critters in it. THose things raise nitrate to the skies. You need it in the 20's or below, not topping 80.

I have used a sump to hasten setup, just attaching the old sump to the new tank, and it does help. But not if the sump is a nitrate factory. You do have a skimmer down there, right?

 

[crownvic4life]

Thank you for your help!

I do have a skimmer (I edited my original post with a link to what Im pretty sure we have) and there are 2 pumps in the refugium. I was planning on thoroughly cleaning the skimmer, and was planning on cleaning up the pumps really well while I have everything broken down. There is a bag of carbon that sits on top of tray of filter floss, which is above the bio balls. Is there a better way of filtration? I read your post about filter socks and cheato (not sure if I could make cheato work in the space I have beneath the tank) but I can look into it for sure.

Also adding in water parameters; you were correct about high nitrates, 80, (I had attributed that to the infrequent water changes, which as we are short staffed are more frequent but still not often enough), ammonia and nitrite 0, ph 8.2, sg 1.025

 

[Sk8r]

Live rock/sand filtration, with a strong water flow. bacteria in the 'live rock' process the nitrate to nitrogen gas which floats away in bubbles. Carbon that's over 2 weeks old, filter socks older than 5 days, and bioballs and filter pads all accumulate nitrate with NOTHING to process it, so it builds up and up. Neither fish nor corals like nitrate. SO the more you can lean totally on live rock with a strong water turnover, the happier everything is. We have a sticky up there [top] called SETTING UP, with a real complete explanation of how these rock-reefs work and how to keep them healthy.