Will a koi start growing when it has more room?

You have had a Koi for 5 years and it's only 5"?????? I would say it's what ever you feeding it that is hasn't grown. If it is well fed it would have busted through the 10gal. tank by now. You can not stunt a fishes growth by having it in a tank that is to small if it is fed right. They need more then just little flake food.Yes it needs a better diet of foods. you should have been feeding it Koi pellets that are specially made for them. I have 3 Koi in my pond that are all 1 1/2 years old and they are all 17"-18" Long. I feed them the floating Koi food that you get at the store. They need high protein food in the summer and high carbohydrate food in the fall . A high Cab diet puts weight on them so they can make it through the winter months during hibernation.

Koi get their best growth in their first three years of life, but continue to grow somewhat throughout their entire life, if space allows. Therefore, your koi will never be huge, but will grow somewhat - especially if you feed a high quality koi kibble and supplement with plenty of fresh fruit, veggies, and protein snacks like brine shrimp and blood worms (and even teh occasionaly boiled egg yolk).

To get optimum growth, it is best to feed several small, high protein meals daily - especially while the weather is warm. As the weather cools off, you can reduce the number and size of the feedings and increase the ratio of carbs/veggies to protein.

One thing about moving a koi from a small home to a large home: the swim bladder controls the fishes ability to control it's depth, and it, in turn, is controlled by a muscle. If you drop a fish that is only used to going up and down in 10 gallons of water, into 100 gallons of water, you may likely see the fish's health suffer as a result.

Think of it this way: say your bedroom and bathroom are on the ground floor, and your kitchen is on the 10th floor, and you climb up and down ten stories every day,. Now, all of a sudden, we've moved your kitchen to the 100th floor, and you have to climb all the way up there to eat every day! You'd be worn out, too!

So, it would be best to condition your fish over time, to the size of his/her new home, by moving up to a 25 gallon, then a 50 gallon, then 100, etc. If you can't do that, perhaps you can section off a portion of the new pond to let the fish build up it's swim bladder muscle in a smaller area, before letting it go out to the pond as a whole. Plenty of fish do just fine without this step, but I'm just saying be prepared, just in case....

Hope this helps.

yes it will grow, you should also give it some freeze dried , frozen, and live brine shrimp and blood worms to encourage healthy growth

My thoughts ?...probably stunted.

You should see some growth ... but will never reach its full potential.