Were you told your water was high in heavy metals by a water company? Can you get info from your water company on the specific heavy metals in your water and their ppm's? Seachem Prime will convert heavy metals to salt but it's limited on how much it makes safe.
I'd run two of those filters if you are going to keep Cichlids.
Re: Prime dosage
We apologize for the delay in response. Upon closer inspection of the Water Quality Report that you provided, one can notice a few things. First, please note the change from ppm to ppb for lead and nickel. The amounts reported as detected averages in a survey of homes supplied water tested by 3 facilities are as follows:
Copper = 0.07 - 0.92 ppm
Lead = 1.2 - 4.0 ppb
Nickel = ND - 1.3 ppb
This would be the average range detected for the Miami area for the year 2008. The area water for 2009 can be assumed similar in composition. These values, unfortunately, do not describe the form that these metals are found in the water.
The Action Levels (AL) are as follows:
Copper = 1.3 ppm
Lead = 15 ppb
Nickel = 100 ppb
If more than 10% of the homes surveyed for copper and lead test with numbers above or at the AL, then water treatment facilities must take action to reduce levels. Every county report lists the AL in one column, then lists the detected levels in a separate column. The detected levels and the AL are not the range for the water report. Limits are the concentrations set by the EPA; so, typical values will be values below the EPA limit.
Also: the drop in pH required would be in the acidic range of pH (below 7.0). The lower pH goes/drops in an aquarium, the more available/soluble heavy metals will become (it will also depend upon many other factors in an aquarium environment).*
To answer your other question about Prime and heavy metals: the standard dose of Prime (1 mL/10 gallons) will remove:
Copper - 2.6 ppm in 10 gallons
or
Lead - 8.5 ppm in 10 gallons
or
Nickel - 2.4 ppm in 10 gallons
We say "or" between each because that is the maximum amount of each that can be removed assuming none of the other components are present. So for example, one could remove 1.3 ppm of copper and 4.4 ppm of lead or any other variety of differing ratios between them. The relative order of preferential removal should be in the order of lead, then copper, then nickel.
This was taken off Seachem's website from what appears to be their technician.