help please.

Yeah vinegar would work too. I think bleach would be good, and then fill the tank with freshwater and add a TON of dechlorinator in it tho neutralize it. You's prob be ok just starting a cycle, but I'd want that crap from the tap water out to help prevent future algae prob!

 

Oh yea, welcome to 3reef by the way. I would suggest not adding anything to your system until you have really researched it. Somethings are just a PITA to get out.

http://www.3reef.com/forums/new-hobby/ultimate-newbie-guide-86462.html

 

If it were me, I'd shut it all off, drain, clean, and start over, but I'm new to all this. It really is a great find, as far as tank size and equipment goes. If, you've never been interested in this hobby, then it's a terrible find. Because now, you'll get hooked.

And welcome to 3reef. Great answers and help await.

 

Can i just change the water with NEW SALTWATER and ro di? Or do i really have to remove rocks and sand too?

 

You don't have to remove the sand or rocks if you don't want to. I would try your best not to disturb the sand to much though. You can just start replacing water with RO/DI water through water changes as well. When you turn the lights back on, I would expect algae outbreaks as well though. I woul recommend ordering a CuC from reefcleaners.org fairly soon to help you out. All the things that were mentioned in previous posts were to try and make life easier for you in the long run.
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I mean you no offense or insult but have you researched salt water aquariums and their upkeep? They are a beautiful thing and the size of that tank (125g) is beautiful when setup right (its the size i have). However, salt water tanks require a lot of work and dedication and especially one thats been so neglected. Its not something you have spend a few minutes here and there and have something so magnificently wonderful to look at. With some good ole elbow grease, time and research, trial and error, patience and persistence (cough,, money) you can find the pot of gold that was left for you at the house. Just dont get into this thinking its quick, easy, cheap and relaxing as those actually are the opposite from what you will experience for some time to come (so far for my experience anyway)....

its kinda like the house that wins the yard of the month in your area, that yard doesnt become so wonderful without hard work, effort and money ...

Cleaning the tank and everything in it will truly assist you in the long run.. The option is yours but go into knowing that either way is going to be a journey, but potentially less obstacles and hurdles will be in your way to obtain a successful end result should you start from fresh.. No its not easy but at this point neither way would be...

Just my 2 cents worth, but then again, I am new to this as well....

Good luck and welcome...

Psst: bookmark this forum as it will become a valuable asset in your future if used in the right way...