One week ago, Monday, I completely drained my (one month old) new pond, and refilled it, with OUT adding salt, this time.
Even though our local pond store recommends 1lb salt per 100 gallons, my theory - after reading the recent "Salt" thread and following links to learn more - my theory is that that salt is what was killing my plants and preventing my bog filter from working as it should.
It's only been one week, and that's not enough for a true test. But already I can say that all the water lettuce and hyacinth I've put in, which previously would have started dieing within a few days, it's all healthy and doing great, the snowflake and hawthorne are growing, and it looks as though plants in the bog are going to thrive, too... iris is already sending out new shoots.
If it's true that salt is what was killing my plants, I'm pretty angry that the "pros" recommend using it.... Salt MAY have beneficial effects on fish, but the pond store people should inquire about whether or not you have plants, too. I've suffered major problems and disappointments with the pond over the last year, and eliminating the salt a long time ago would have solved all that.
Oh well, by now it's water over the damn. If removing the salt will save my plants, from now on, I'll be a happy ponder.