new here, cycling question

[Liebernoodle]

Hello, i'm new here so here's my first question! :D

I'm starting a brackish tank for a Green Spotted Puffer. The tank he or she will be moving into was a fresh water tank until today. This is what has happened..

after the FW fish were removed from the tank (and donated to a new home :) ), I removed all the gravel from the tank. I then removed about half of the water. Oh by the way, inside the tank is a fake rock and little hideout place (also made of plastic).

I decided to use sand instead of gravel this time so I put the sand in the tank. Then I filled the water back up, but this time with water from a SW tank that has already been cycled and in use. This made the SG 1.005.

I did the tests and came up with 0 ammonia and 0 nitrate. So i'm not sure if this tank is cycled or not..

To sum up the variables: In this tank is the HOB filter, two plastic decorations, and 1/2 water from a FW tank. It also has 1/2 water from a SW tank. Finally the sand and heater is brand new and has never been in an aquarium. Could this tank already be cycled in that case?

I thank you and my future puffer thanks you :)

[OrionGirl]

Possible, but not likely. Using the 'used' water won't really help, as the bacteria are not in the water column. The bacteria from the FW tank may still be present in the gravel and on the decorations though.

I would challenge the tank with some ammonia--get it up to about 2 ppm, wait 24 hours, and test again. If ammonia comes in at 0, test for nitrites. If they also come in at 0, the tank is cycled. If not--fishless cycle with the bottled ammonia before introducing the puffer.

[cdawson]

I agree, the tank is probably not cycled; adding the water is pointless. All you're doing is putting in dirty water, I'd check for nitrates because it could be off the scale if you took that water from an established tank. Especially if the water needed changing.

As for any bio bacteria living through all of that, I doubt it because SW bio-bacteria is different than FW bio-bacteria and such a large drop in salinity would have killed them off completely.

[Liebernoodle]

thanks for the input. I'm gonna do a complete fishless cycle to make sure that mr. puffer won't die. Better safe than sorry!