Brackish aquarium help

[Mapleleaf24]

So my roommate recently got me one of those complete 20gal tank sets from petco and I got a Columbian shark catfish. So far the tank is setup freshwater but id like to transition it to brackish for the fish.
So i was just wondering what was the best way to do this.
My roomate's brother just said to use crushed coral substrate instead of gravel but I just want to make sure.

I am also going to be getting a way bigger tank in the next year because the fish gets rather big

tank-mates?

 

[CLDarnell]

Hello and welcome to MFK!

Congrats on the tank

First off, that fish is going to get big. Really big. Once he is adult, your tank will need to be full salt. You are correct that he should be in brackish now. Being a big fish and also a very active swimmer, you are going to need a true monster tank eventually. 125 is most likely recommended for an adult size. Also, he will become very carnivorous and will most likely eat anything smaller than he is. Is there anyway you can return the fish? He isn't going to be a good starter fish long term. Plus, you need to do some things to your tank before adding fish (read further).

To sort of answer your question, I recently changed one of my 29 gallon tanks from fresh to brackish. I bought a small bag of aquarium salt at Petsmart (Oceanic Natural Sea Salt, 1.45 lb bag) and a hydrometer. Actually I bought two bags, but 1 was all I needed. You will want to add the salt (without the fish in it tank) slowly and continue to check with your hydrometer. Your hydrometer may need to be "seasoned" (basically, fill it up with brackish water and let it sit for a few hours). At this point, it should start giving you accurate readings. I run my tank at 1.008 salinity and keep 2 leapord puffers and 2 Archer fish.

You should do a quick search on cycling a new aquarium and read up on it before going further or adding fish. You can search here and on Google (use keywords "nitrogen cycle aquarium").

Keep posting back with questions...and good luck!

 

[Pufferpunk]

They are also schooling fish, so a school of 18" fish are going to require a HUGE tank!

 

[Mapleleaf24]

thanks for the advice guys, ill definitely have to get another one and work on getting a huge tank in the future and thanks for the help on turning my tank brackish

 

[Pufferpunk]

Good luck with them. A school of these adults are very impressive!