I have two Turtles: Yui ( the one i'm asking about the tank and shell) and Bob (its ok to laugh at the names people do

)
Ok, thank you, i will measure the tank. Like i said its now been at least over a week since i touched it except for the filter which i just recently cleaned. I'm planning on giving the entire tank a good cleaning outside down to, well everything.
I need a new filter which I'm aware of for Yui cause the one i have now doesn't run well with the size tank i have. I want to buy the same filter i have for Bob, for Yui since both their tanks are very close to the same size.
I was confused because i was running Yui's tank the same way as Bob's and his tank has been fine and clean. It's always been fine for a couple years now unlike Yui's tank. i just was looking at the heater in it yesterday and apparently its broken. I don't know how this all happened at once but it did.
I feed them both the same way except:
Yui: Is fed "Reptomin" from Tetra fauna and "freeze dried river shrimp" from Fluker's
Bob: Likes "Reptomin" but barely shrimp. My brother has tried feeding it blood worm without me knowing, he feeds it to his fish to. My brother said he likes it.
I have yet to try feeding lettuce to Yui but i know for a fact Bob does not like his veggies, ha. I've tried laying it on the dock and laying it in the water, he lets it sit there and i end up having to take it out myself later.
Shopping list:
New Filter
New heater
Anything else?
Now the terms of the territorial subject. When i first received Bob back in probably 06' or 05', he had a younger brother, so to say from the teacher i had got them from. I had them in the same tank and they got along. I do not know if they were put in separately though prior to before i got them. But i assume they were always together if they always got along. The younger brother died from a sickness that i did not know he had when i had got him. So bob has been left in the tank solo for around 4 or 5 years. Ever since he's become territorial and because of that i don't believe it would be possible if it was another turtle besides his younger brother.
I will check to see if the rest will rub off. If not i'll have to find some other way to clean her shell better. A family friend had given me a shell hardener cream which was working nicely and keeping the shell nice as well, i don't have anymore though.
Feed back?