How much Dupla fertilizer to use?

> From: steveb at bga_com (Steve Benz)
> According to the box (or what I can make of Dupla's attempt at
> English), I'm supposed to put in 1 tablet per 50l of water, my tank is
> about 200l, so that's 4 tablets.

The DuplaPlant tablets should be added according to tank volume when
the tank is first set up.  After that, they are added at water changes
(biweekly is a good schedule).  Add tablets based on how much water is
changed (Hint: if you have 20 liter size tablets, change water in
increments of 20 liters; if you have 50 liter size tablets, change
increments of 50 liters).

> And I've heard alot of people say that the drops are necessary, but only
> needed in very small doses - I believe George B. said that he only uses
> 2-3 drops/day in his planted 75's.

Yes, the drops compliment the tablets.  Drops have trace elements
(mostly iron) that will oxidize quickly.  I dose as follows:
  85g tank  - 3 drops per day
  90g tank  - 3 drops per day
 100g tank  - 4 drops per day
 120g tank  - 5 drops per day

How much the tank needs will vary with the setup and inhabitants of
the tank and may change over time.  We measure iron monthly and adjust
the dose to maintain 0.1 mg/l (based on the Lamotte iron test kit).
> But even after putting in a double dose of both I'm barely getting any
> hint of a reading out of my Red Sea fish pHarm ltd. iron test kit.
> >From what I can get out of reading the Optimum Aquarium, I should
> have iron in the .2 - .3 ppm range.

My personal bias is to not trust hobbyist grade test kits.  

Be careful of adding too much stuff.  An overdose of trace elements
can be just as bad as too little.

> Is this right?  I thought perhaps my test kit was faulty, but I found
> that if I crushed some of the tablets or put some diluted drops
> directly into the tube I could get positive readings.

I have found that, with the Lamotte kit, 1 DuplaPlant-24 drop in a
gallon of distilled water will provide about 0.15 mg/l of iron.