Turtles DO need water heated between 70-80F they need a dry basking area with a basking light to heat it about 10 degrees hotter than the water.
A good canister is a must turtles produce a lot of waste so you have to over filter
A 29 gallon tank isnt big enough for 2 turtles. they need at least ten gallons of water per inch of turtle.
goldfish arnt good food for turtles and they probably will be eaten even if the fish is bigger then the turtle they'll still take a bite and that will lead to the death of the fish. Also goldfish produce alot of waste that will increase your filtration needs
in addition to goldfish being coldwater fish so I imagine they wont be happy in warm turtle water.
turtles need a varied diet of heathy greens and veggies, live food, and pelleted food
turtles absolutely MUST have a UVB producing florescent or Mercury vapor bulb
with out this light they cant absorb the calcium from their food.
also with 2 turtles you'll need more than 10 gallons per inch or turtle because they are territorial and will need a buffer area to setup their own territorys.
My Turtle is a 9inch female red-eared slider. she lives in a 120 gallon aquarium with the water filled about 3/4s of the way up
(these turtles are swimmers and need all the water they can get)
I made her basking area by bending a peace of plexi glass so it looks like a flat platform with a ramp (blow torch needed for that) I used plastic hardware cloth and zip tied it to the plexi glass so she can easily climb up to bask.
a regular 60watt house bulb is used to heat her basking area.
a 24inch Exo-terra repti-glo 8.0 positioned over the basking area provides her UVB
I use an acura heater to keep her water warm
my filtration is a Filstar xp3 and a lifetech 828 canister filters.
she eats collard,turnip, and dandelion greens, a little romain as a snack (no nutrition in romain so its used as a treat only) she loves carrots and they provide vitamin A that helps keep her eyes healthy. I use rosy minnows every so often to feed her . and she gets a mix of wardley,repto-min, and mostly exo-terra aquatic turtle diet. I also want to try the aquatic turtle diet from mazuri for her.
as a side note petstores are lying when they say the turtle will only grow to the size of their tank, total myth the only think that stunts them is the improper care they often receive .
when I adopted mine she was 8 and a half inches living in a sludgy 30 gallon tank were she could hardly turn around
I would go for the biggest tank you can afford because buying a small one and upgrading gets expensive.