The addition of a good, properly working filter will improve the conditions in the tank and the fish will benefit from it being there.
You should not have goldfish and platies in the same tank ever.
It is important to remember to put things in a goldfish tank, even goldfish get bored. Some of my suggestions for tank decor are artificial plants and a "hidey hole" for your goldfish.
No, shrimp and goldfish should not be kept together in the same tank as goldfish may eat the shrimp.
No, cherry shrimp should not be kept with goldfish in the same tank as goldfish are known to eat shrimp.
no. you should have 10gal of water per goldfish. you shouldn't have goldfish in a 5gal tank at all. they are huge waste producers
NO
an aquarium or a fish tank
Once a week :))))) i have experience
It's a possibility, but a goldfish and a platy should never be in the same tank as they are not compatible, and their needs are different
Yes
Fantail goldfish are a hardy breed, strong swimmers and they compete well for food with the ryukin, shubunkin, comet or common goldfish; making these goldfish breeds good tank mates for your fantail goldfish.
No, first of all they should not be in the same tank, and secondly, goldfish are egg laying fish so they do not get pregnant