Q. My fish pond holds 600 gallons and is about 3 feet deep. The top part of the fish pond waterfall is a 70-gallon tub and biological-vegetative (plant) filter. All summer my fish pond is crystal clear to the floor. The water hyacinths in the filter are about a foot tall, and I had 30 to 40 flowers in the late summer. The top shelf of the pond waterfall flows into a container of lava rock, which is slotted on the bottom to allow water to run through. The water then passes through the hyacinth roots and flows down into the fish pond.

I got the idea of a vegetative pond filter from something you wrote in last year's Aquarium Fish International.

When I put in the fish pond we used a butyl rubber (roofing) liner. I was cautious though. I took a 1-inch square of rubber and put it in a container with three guppies. They were dead the next morning. I put a 1-inch goldfish in and he was dead in an hour. So we bought a Tetra liner to replace it. Imagine my pain if we had used the roofing liner without checking.

A. The vegetative pond filter is something I have recommended for years (glad the article gave you some good ideas) and use them very successfully in my ponds. It provides beautiful flowers for the dinner table and attracts wildlife while cleaning up the pond water.

Water hyacinths — a floating plant — are excellent for vegetative pond filters. Their long, dense root systems do a great job of mechanically filtering the pond water. In fact, they do such a good job that you may want to remove them occasionally and rinse them off. Of course, they also are very good at removing nutrients that algae would use.

Bare root iris will also do an effective job. They tend to get started earlier in the spring and work later into the fall than water hyacinth.

Your liner story certainly was a close call. Unfortunately, the excitement of getting the pond up and running and stocked with fish drives many hobbyists to ignore sound practices — such as testing uncertified liners.