10 Gallon second tank stocking and decor ideas... Possibly salt water?

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I tried this once before and was horrified with the results. I did not do a lot of research before hand. I used the same size tank and the male was ripped apart by the female overnight. They all seemed fine each picking an area of the tank to call their own, but i guess things went sour after sunset, when I looked into the tank the next morning the female was hovering above the male's dead, mangled body. Plus unless you can sex them yourself or really trust your lfs those females could be young plaket males (the ones bread with short fins for fighting; their fins look like a female's fin set)

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They are doing great, the females school and almost seem to play together, the dark female and male will sometimes school but no nipping from what I have seen. I actually was given a 23 gallon nano tank with a stand so I have transferred them to there and added one albino cory (yes I know they need a school, I am waiting on 2 more, may add more later) and a African dwarf frog that was given to me. It is an awesome tank, the bettas seem to have a very odd relationship for "fighting fish".
 
Also, the three females have egg spots so i'm sure they are female. I did alot of research before attempting and made sure my male did not have a very aggressive personality before adding females.
 
^this
I tried this once before and was horrified with the results. I did not do a lot of research before hand. I used the same size tank and the male was ripped apart by the female overnight. They all seemed fine each picking an area of the tank to call their own, but i guess things went sour after sunset, when I looked into the tank the next morning the female was hovering above the male's dead, mangled body. Plus unless you can sex them yourself or really trust your lfs those females could be young plaket males (the ones bread with short fins for fighting; their fins look like a female's fin set)

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That happened with my uncle once. Got a male and female betta in to small of a tank. The female killed the male.
 
Yeah they are all in a 20 gallon and doing great, I wasn't planning on the upgrade it just happened Lol.
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yeah it does look nice and I appreciate the comment but for whatever reason my frog got sick with red spots on his belly and his skin was shedding. Idk what caused it as my water levels are perfect and all the other fish are very healthy... I took him to my lfs and they were not able to explain why it happened but I am doing research now to figure it out as Id love to give it another go but I hate loosing fish so I will try and see what I can do different so not to loose another if I get one.
 
Does the frog have red legs? Is he or she eating?
 
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