First you need to get some chemicals. Go to Greg Watson's web site at
http://www.gregwatson.com/
Order 2 pounds of CSM+B. Plantex CSM is a trace element mix that also contains iron. Greg puts some Boron in it and calls it CSM+B
Order 2 pounds of potassium nitrate and one pound of monopotassium phosphate.
Tom Barr is the guru on adding nutrients. He will probably say to add:
1 to 2 ppm KH2po4 twice per week
10 ppm KNO3 twice per week
and between .1 and 2 ppm Fe.
For phosphate:
In general to get 1 ppm PO4 from KH2PO4 use 53.9 mg per 10 gallons. For 150 gallons thats .8 grams (twice per week)
For Nitrates
To get 10 ppm NO3 from KNO3 in each 10 gallons of water add .62 grams of KNO3. So for 150 gallons add 9.3 grams KNO3 twice per week
For Fe and traces.
First mix a concentrated solution of 47.8 grams of CSM+B to make 250 ml of water.
.6 ml of concentrated solution to make .2 ppm Fe in 10 gals
6 ml of concentrated solution to make .2 ppm Fe in 100 gals
30 ml of concentrated solution to make 1 ppm Fe in 100 gals
45 ml of concentrated solution to make 1 ppm Fe in 150 gals
22.5 ml of concentrated solution to make .5 ppm Fe in 150 gals
I would go with the 22.5 ml to make .5 ppm Fe (twice per week)
Once per week before you add the chemicals do a 50 % water change to reset the nutrient levels.
The above is all you need to know about nutrients.
The Ca and Mg and KH and GH is another issue.
This is probably for 3.5 Watt/gallon and less. Otherwise all bets are off. Reduce the lighting.
email me if you have any other questions
Steve Pituch