I guess tom barr was correct. The walsted setup runs out of nutrients after a year.
Boy, I sure hope you're right, although one of my NPTs scooted right past the one year deadline without a hiccup in leaf production. But if things slow down, I'll be able to forget about weekends like the last one where I spent at least six hours pruning and thinning back the growth. It was getting so bad even the Corys were having a hard time getting around.
In addition to the methods Diana mentioned, another way to put the brakes on plant growth is let the water get too soft. There's something about Calcium and Magnesium that plants find essential for growth, so if you want less work on weekends, stop checking the water hardness.
Another thing I've noticed is that some plants do better at different stages of NPT maturation than others. For instance, in one tank the Hornwort, Wisteria, and Ludwigia Glandulosa grew at a tremendous pace during the first four or five months. One of my chores this last weekend was to remove all their traces since they were obviously being choked out (allelopathy?) by the Swords, Ludwigia Repens and Bronze Crypts. I've never seen 18" Crypt leaves before. Guess I'll have to start pruning them next.
If this pruning continues to get out of hand, there's always a return to the hi-tech methods of changing water, cleaning filters, injecting CO2, dosing ferts, swapping in fresh light bulbs, testing for ammonia and my favorite - vacuuming gravel. Those were the good ol' days.