just out of curiosity, how are you determining "as needed" ?
ohh the eye method of course.
1. Dip uncleaned hand into the aquariums water column, about half way down
2. slowly rotate the index or pinky finger, no other.
3. 30 seconds later remove the chosen finger and press firmly against the eyeball, allowing full contact with the saltwater soaked fingertip.
4. Over the next few moments while in discomfort, feel for the following
- Stinging (Alch)
- Burning (Mag)
- Fizzing (Cal)
- Watering (Stron)
If any of the elements are missing, thus the reaction in your eye not being present. Dose accordingly then repeat the test until desired levels have been achieved.
:D