cleaning up a used tank

hello, newbie here.
my wife and I bought a 55 gal tank and stand/cabinet that was originally used as a freshwater aquarium. we have cleaned it up with just water (and it was very clean when we got it), but is there anything we need to clean it with to sanitize the tank before starting a marine aquarium in it?

Also, it came with some rocks and stuff. most of which we discarded. but there were a couple larger beautiful rocks. not sure what kind of rock they are, but they are very porous and open. I've read that any rock can become "live rock" if its in your tank long enough, and I think these would make great rocks for that with all the holes and stuff that is in them. they do appear to have some green algae looking stuff on them. how should I go about cleaning/scrubbing them so we could use them in our saltwater tank?
thanks!

 

If your planning a reef tank, I would make sure that tank was not dosed with copper before. You can ask the original owner, but if you can't, your taking a risk. I would use acetic acid to clean it, get any residue off. As for the rocks, as long as they aren't silica based, you should be fine. I would bleach any rock and clean it really good.

 

Just take some water and scrub then let dry, since its a new tank it will actually help cycle after you scrub it off and dry. As far as the tank I would static test it but then also add a little bottle of white vinegar and throw a powerhead in it and let it sit for 24hrs that way you know its good to go and plus no leak test.

 

how can I tell if they are silica based rocks?

 

Common distilled white vinegar is a very good tool for saltwater use. I use it straight for cleaning equipment like tanks, filters and powerheads, it leaves no harmful residue and is safe enough to stick your hand in or splash on you. The low pH dissolves calcium deposits and makes things look like new.
It will also tell you if your rock is true ocean or calcium/coral based rock. Pour a little vinegar on the rock and it should fizz like crazy if its calcium and do very little if its normal rock not calcium based.

 

so if it does not fizz when I put it on these rocks, does that mean they are silica based and I should not use them?

 

Don't know that it would specifically be silica but it would not be calcium based which is what you are looking for in a saltwater tank. What color are the rocks? If they are not white they could be volcanic based and contain iron among other things. I have seen vendors take volcanic or other soft rock and cut it with a water jet to add holes and caves.

 

Basically silica based rocks are rocks you'll find in your backyard such as granite, mica etc. If it looks shiny or has some shiny speckles in it, even very tiny, it most likely is silica based. But that test with the vinegar should work, as it will dissolve the carbonates in the rock. Volcanic rock is also not good to use as it will leach iron and other heavy metals and compounds into the water resulting in incurable algae issues.

 

they are kind of a light gray color (under the growth thats on them) and seem to be somewhat of a soft stone. I can get it to crumble a little bit at the edges with some effort. I'll try to take a pic later on post it on here.

 

sorry, didn't have time to upload a pic last night. but upon closer examination these rocks do have some small sparkly pieces in them. very very small sparkly's but they are there. so they are probably silica based, right?