How to maintain iron levels?
 

I've been adding iron and trace elements to my 15 gal. system. What's some
good tips on how often to add and how much I can allow the iron to drop
before adding again? After my first dose I had about 3.0, two days later I
have 2.0..at what level should I replenish? I do a water change every week,
could it wait that long without affecting the plants??

Thanx alot.