Hello Abby,
First i want to start off by saying that you may not actually need to separate them. they may have been fighting because they were in a 'crammed' situation. *i am not sure what their living arrangement was before the plastic tubs.* but if they were crammed, that may have been their reason to fight. turtles are pretty territorial and if one thought that the other one was cutting into her/his territory, he/she would attack the other one.
If you really feel you need to separate them... the cheapest would be the tub idea. but a more expensive route includes LARGE tanks. the 'rule of thumb' is 10 gallons of water per INCH of turtle, which would mean that you would need 60 gallons for one turtle and 80 for the other. (this doesnt mean that they can't survive in a smaller amount of water) but you do want to make sure that they have PLENTY of room to move around, and they love to swim, so you also want to make sure they have enough water to swim their little hearts out!
Depending on what the sex of your trutles is... the males get about 10 inches (i believe.. not too sure on this) and the females can get up to about 15 inches... so if you plan on keeping these, you will eventually either need a VERY LARGE tank... or a pond!
about the divider: i would say that you could use a piece of plexiglass (though im not sure this would hold that large amount of water back)... i would say probably not if it were up to me. You could always cut holes into the plexiglass so that water can get from side to side (this means u would only need one filter), but make the holes small enough that the turtles cant reach each other... you could probably connect it to the glass by using the stuff they used to put the tank together... i think it's called aquarium glue or something.
The easiest thing that i have heard of for turtles to bask is a turtle dock. but if you're turtles are 6 and 8 inches, im not sure one of these would hold your turtle up out of the water. of course, if you do go this route, u will need 2 docks (one for each side of the tank and turtle).
the water should be as high as you can get it without the turtles getting out... they LOVE to swim, and they love having room to swim. the more water you can give them, the happier they will be!
if you want to keep the water pretty high, you will need a cover for the tank, u can either buy one of these or make it *not sure about buying directions*...
You also need a basking light(this can be a regular light bulb), and it should be directly over the area they bask on. this should reach temperatures in the mid 80's. you will also need a UVB light. and you may need a water heater, depending on where you live. the water temps should be in the mid 70's. I hear that the heaters with the glass covers are best so that your turtle can not get burned if he/she would happen to rub against it!
as far as filters, all i know is that you will need a BIG ONE for such a large amount of water. i know that people on here make their own, so that might be best in your situation, i am sure if you ask they would gladly give you directions for making your own canister filter!
your turtle (at this age and size) should be eating MOSTLY greens, which can include anything from veggies to fruits (especially dandelion greens, collard greens, red lettuce, broccoli, carrots), and it definitely should be a VARIETY of food... your turtles should only be given the pellets like two or 3 times a week. this is protein, and considering they are supposed to be mostly vegetarian, they should only eat it a few times a week. you can offer greens at ANY time. also, to cut down on waste for your filter it is A LOT (speaking from experience) easier to feed the turtles in separate containers so that most of the waste is NOT in the tank.
if you do feed your turtles mostly reptomin, you are probably overfeeding them, which could cause them MAJOR health problems later on in life! which i am sure you do not want. i hope this information helps 
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~ Evie 
Pets:
RIP 0.1.0 German Shepherd {Dusty}
0.1.0 German Shepherd/Collie mix {Shadoe}
0.0.2 RES turtles {Booger & Snot}
1.0.0 African Clawed Frog {Bingo}
0.0.2 Snail {Gary & Larry}
