I believe that even the smallest aquatic turtle (map) gets up to 8 inches at maturity.

Your 150 gallon pond is too small for the 3 koi + 3 goldfish (they get BIG)

Turtles carry salmonella. I would nix that idea in a heartbeat. Your pond also would need a place for a turtle to sunbathe and also be "fenced in" so that the turtle couldn't escape.

Turtles can be fun pets, they will eat small fish. I agree with Heather regarding a fence. Turtles are nomads and they will move around from place to place. Also, they do need a rock to sun bath on.

Regarding the nixing...I would not say that. I would be sure that your kids learn about proper hygiene and if they touch the turtle after playing with it they need to immediately clean up with an antibacterial soap. I see no harm in having a turtle as a pet. Just educate yourself about how to care for them and how to be safe without getting sick.

I had one for years here, it was not a pet and came on it's own. My pond does have rocks so that it can sunbath. I've not seen it now for the past couple years, so he/she must have moved on and I'm ok with that.

Turtles should not be something you just jump into without researching. They do have more specialized requirements than fish. They require more filtration or you'll have a horrible smell. Their food and droppings requires frequent cleaning even with great filtration. They do have requirements for containment and basking too. There are also problems with non native turtles escaping in some parts of the country. They can and do dig and climb. They aren't that easy to contain.

I'm sorry but your pond is too small for any koi let alone three plus three goldies. For proper health koi should be in ponds over 1000 gallons and 3 feet deep....

Thanks everyone. No turtle.
I guess I'll have to give away the koi when they get too big and just keep the goldfish. No room for a 1000 gal pond in my tiny yard.

I had a turtle in an aquarium for five years as a kid and my father still complains (forty years later) about how bad it smelled when he had to help me clean the filter....

I like my fish but I looove my turtles. If not for them, I would not enjoy the pond half as much. But, turtles are the reason I built my pond in the first place. :)

All reptiles, amphibians and birds have salmonella naturally in their bodies, that should not be the reason to avoid the turtle. As stated previously, proper cleaning and hygiene makes this a non-issue. It is true that if not contained the turtle will probably look for another body of water at some point. It's also true that your pond is probably too small. Adding a native turtle and giving him a choice whether to stay or not could be entertaining for a short while but upsetting when/if the turtle moves along.

LOL Have you ever seen many kids voluntarily washing their hands all the time? Not going to happen!

Parents need to parent. Thought that was a given. I have kept frogs, toads, snakes and turtles nearly my entire life and have not contracted any illnesses. My kids, now 10 & 6 have also had frogs, toads, lizards, turtles and snakes their entire lives and also have not contracted any illness. We are not perfect about washing after each handling but we make an effort. Salmonella tends to be a problem with animals kept(or mis-kept) in less than clean conditions.

Sounds like you've already reached a decision based on your particular circumstances. That acknowledged, I agree with the above advice with the exception of the antibacterial soap business (causes more harm than good in the long run)in which case I defer to rsingley & whole-heartedly agree. The fact that I've survived all these years is proof enough for me;)

Turtles are a pain to corral but that would be the ONLY reason to deter me. I'd welcome one if he showed up of his own accord (provided he didn't eat my fish for dinner). I'd try & steer kid's attention in another direction without discouraging interest in the pond environment. Losing a pet is hard at any age and you're alreading facing giving away the 3 koi at some point...

blessings & happy ponding,
~digger