Switching Tanks USED and Adding in NEW Tankmates

Sep 3, 2015
american / nv
HELLO!! I'm fairly new to owning fish, but recently I've gotten really into it! I've never really used a forum like this so I'm sorry for any mistakes made..
Okay, so when my boyfriend and I got our fish we never realized until recently how dumbly? we went about it.. We pretty much were like 'YEAH OKAY LETS GET SOME FISH' and threw them in a dirty old tank pretty much without any basic necessities ( no wonder my fish died so quickly when I was little.... ) I don't know how our fish survived!? It was ridiculous looking back on it...
Since then we've grown up a lot, though! We ditched the dirty little tank and currently have a 40 - 50 gal tank but we're moving our fish into a, what we think is a, 120 or 180 gal tank seeing as they're going to live a long time ( hopefully ) and are known to get quite large. I was wondering about how many fish should we keep in a tank that size? We're considering getting one more to add into our community ( possibly an eclipse catfish, oscar, peacock eel, or black knife ghost?? my boyfriend wants something that swims around more, something special or "exotic" ) We considered another Bichir or Pleco but I read they can sometimes be aggressive with each other? So I'd rather not chance it. ANYWAY OUR CURRENT LINE UP IS Dinosaur Bichir (6in), Sailfin Pleco (6in), Striped Catfish (4in), and a shy Pictus Catfish (4in)! They're fairly friendly with each other!! (plus a random assortment of minnows / snails / ghost shrimp) I know if we are to get another it'd need to be a decent size due to the possibility of the Bichir eating them. ( found that out the hard way with some beautiful guppies.. )
I was also really worried about our new tank ( it's used.. ) we aren't sure about what was previously stored in it ( it has scratches ALL over it ) ANYWAY I'm just worried about possible diseases still in the tank?? ( IF THAT'S EVEN POSSIBLE idk )

1) What are your opinions on if there's enough space or which fish would be better for our tank? ( I know they have a guide for it, but I don't really understand 1" of fish for every 12 sq. in I'm terrible at math.. )
2) My boyfriend is considering making the new tank covered in plants. Currently, we only have two plants. They seem to do okay but do you have any tips for having a tank like that??
tank 1.jpg tank 2.jpg
3) Lastly, what precautions should we take for used tanks? ( it has no leaks and we already have a new filtration system etc. )


Elite Fish
Jul 19, 2004
Cape Cod
A: If you haven't yet, fill up the tank on a flat, level surface ideally outside or in a garage, and leave it up for a day or two just to verify no leaks. Much easier to find out ahead of time and/or outside. Make sure all is dry on the outside after it is filled up, so you can tell easily if there is any dripping or slow leaking.

B: To clean / disinfect a used tank, you can use bleach (diluted, not straight bleach). Just rinse it out really good afterwards until the bleach smell is gone, and use a dechlorinator when refilling (as dechlorinator will also deactivate residual bleach).

C: Are you putting the new tank where the old one is going? If so, you'll need to just move over everything (fish, decor, filter media) to avoid having to re-cycle the new tank. If you're not going in the same space, you can get the new tank set up and add some used filter media to get it cycled either as a fishless cycle or just with moving stuff / fish slowly over so you don't get an ammonia spike.

D: Don't add any new fish yet or when you're first getting the new tank setup. Let it get settled with the current population and go from there.

I believe pictus cats are social with each other, so a few more of those would be a nice start once everyone is settled into the larger tank. If it were my tank, I'd be looking into something to be more up in the water column as right now you've got primarily bottom dwellers. A good site to research potential tankmates is Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums

E: Plants - you've got a pretty big tank, so sizable plants might work out nicely. To keep things easy, you can just keep lower light, easier plants with pretty much any lighting. Stuff like java fern, wisteria, some amazon swords (which grow very large), don't require any particular effort on your part and don't require strong lighting. And healthy plants will actually make the tank healthier by absorbing some of the nutrients from fish waste.

One of those example tanks you pictured has that grass look all over the bottom - you probably won't be able to replicate that type of look with some of the active bruisers you've got. But something like that first picture should be doable. A lot of plecos like to hide in and munch on driftwood, too. There are a lot of plants out there, so make sure to look up each one and avoid anything that requires high lighting or CO2 (unless you're actually prepared to go that route).

Sep 3, 2015
american / nv
Wow!! Thank you for taking the time to type out such a detailed reply!
My boyfriend filled up the tank before one on a level surface for about 15-20 minutes ( he only did if for a short amount of time because he was at the previous owners household buying the used tank ) If I can convince him to drag it out of the room ( it's so dang heavy.. ) we'll do it again for a longer period this time just to double check. We're putting the new/used 120-180gal tank where the old one is, but we got a new stronger canister filter ( 175 gal ) since it's such a bigger tank. We hooked up the new canister filter to the current 40-50gal tank and put the filter media ( or biological filter? ) in it to keep the bacteria so it can spread to the bio-chem stars?? Idk what that means really ( that's just what my boyfriend said ) but it seems to be doing a wonderful job!! So I guess we have it already set it up so it's recycled / ready for when we finally finish cleaning up the new tank!
Thank you for the site link I'll definitely check it out! I've also considered another pictus. ( The idea of getting an eclipse came from us walking around Petsmart and seeing a pictus and eclipse being buddies haha ) I get so many mixed answers on some different sites when it comes to tankmates and temperament of fish.. I personally don't mind the bottom dwellers ( I think they're the cutest!!! ) but especially since we're pretty nocturnal ourselves haha!
We've actually had an Amazon Sword and moss ball for a month or so now!! We also recently got an Anubias Congensis ( we read some things about plecos / snails not eating it? is it possibly poisonous to them?? ) and Cyperus Helferi? I don't know much about them, but they're already in the tank. My boyfriend said he looked them up a little, but I plan on researching them some more too! The pleco and random snails have already chewed up the leaves on the amazon ( moss ball is still going strong!! ) but it still seems to look healthy and grows new little leaves every so often! My boyfriend is the one who initially had the idea of covering the tank in plants (even though they'll probably get tore up haha! ) we both thought the fish might like all the possible hiding spots though! I like the idea and hopefully he'll put good effort into it! Sometimes he can be fickle so you never know! Haha!!
Again thank you soooo much for your reply! You're too kind!!