Indoor pond lets Cedar Rapids couple enjoy koi in all seasons

When Larry and Erma Thompson told their children they wanted to build a swimming pool in their sunroom, the family was excited.

Then they told them the pool would be for fish, not people.

In 2013, the Thompsons took on a unique project - creating an indoor home for their beloved koi.

Now, 25 of the brightly colored Japanese fish keep them company year-round.

'I find it very peaceful,” Larry Thompson said. 'The pond is very tranquil. Koi are a schooling fish and never are aggressive - they just float around in the water and seem happy all the time, so it is very relaxing.”

The Thompsons have raised the fish for years - before moving them indoors, they had two outdoor ponds on their three acre property near Squaw Creek.

On any given day, wild turkeys and deer roam freely through their yard. The heavily wooded neighborhood is a haven for wildlife, which the Thompsons have always enjoyed. But it was causing problems for their fish.

Mink were attacking, maiming and sometimes carrying koi off into the woods. One fish, still swimming in their indoor pond today, had its dorsal fin mangled. They've also seen herons in the neighborhood - the large birds have been known to feast on koi. Another concern was the possibility of losing fish to harsh winters.

None of those are problems anymore, and the Thompsons hope to enjoy their fish for years to come.

In good conditions, koi can live for 50 to 80 years. The biggest fish the Thompsons have is three feet long and weighs around 30 pounds. Each multicolored koi's pattern is unique, like a fingerprint.

'They're Mother Nature's living jewels,” Larry Thompson said.

He said the fish have different personalities - some are friendly and swim right up for a treat when he enters the room. Others are more standoffish. But none of them have names.

'It's bad luck to give koi names. I named one once and it died,” he said. 'I care too much for them to name them.”

He has been raising tropical fish for 50 years, and got into koi later in life. His sister-in-law is a koi judge at competitions.

Working with the fish keeps him busy, he said.

'I worked long hours at Rockwell, so when I retired I thought, well, I can't just sit,” he said. 'At Rockwell I was a computer guy. Now I'm a fish guy.”

A member of the Eastern Iowa Pond Society, he helps organize yearly pond tours and is on 'the Pond Squad” - a group that will go to people's homes to provide advice.

When designing the pool, he wanted to make sure the house would retain its resale value. Not everyone is looking for an indoor koi pond, so the Thompson's is designed to be easily converted into a conventional swimming pool. It is 12 by 24 feet - standard pool size, with steps and both a shallow and deep end. The plumbing, filtration and UV lights are already in place.

Working with contractor Leisure Living and DJ's Pool & Spa, Thompson adapted the pool to be fish-friendly, finding a special pool liner online - most conventional pool liners are designed to inhibit algae growth, but the chemicals that do so would be toxic to fish.

Other concerns were humidity, mold and mildew.

'With 150 pounds of fish in the house, concern was a smell,” he said.

He keeps the air a few degrees warmer than the water, which keeps the humidity down. In-floor heat also dries out the air. There is no fish smell in the room whatsoever in the 1,000 square-foot room, which is lined with windows and sliding glass doors.

Floating on top of the pond are plant islands with peace lilies, garlic and flowering plants. Their roots go into the water and don't need dirt. They add enzymes to the water while pulling out fish waste to use as fertilizer. The rest of the waste goes through a filtration system, which filters 15,000 gallons of water an hour in a closed system. The pool holds 11,000 gallons total.

'I hope I'm not pretentious, but everybody told me it wasn't going to work,” Thompson said. 'But it did. Maybe I'm just lucky.”