Water Source Question (Public Agency)

Some of those tests are done at various locations in the distribution system, such as lead and coppers (which are done at specific sites, with water that has been stagnent in the pipes for more than 6 hours, and could not be 100% representive to a well used tap, or one that travels through different material pipes.)
Hardness I do not believe changes a whole lot from POE (point of entry into the distribution) to user, but could vary if the system is supplied from multiple water sources and treatment processes, I would use calibrated test kits to determine these (see the sticky or post to fert & water parameter forum to see how to do this). Same with traces, they should not change too much.
Where I am, my harness is pretty close, again I use API test kits, which I checked against standards and kits at work. Also I live a few blocks from one of my city's treatment plants.
What is your main concern? Shrimps?

My only concern is that in one of my tanks (6-Gal) my GH is relatively high (around 13), however in my other tank (10-Gal) my GH seems to be ok (around 5-6) and the water and conditions of the tanks are practically identical (In terms of the other readings - pH 6.8, kh-4, CO2 at around 18-20 ppm). The only main difference that I can think of is that the light in the 6-Gal has lower wattage (T5 6W, 9" long) compared to the regular fluorescent light that comes with the 10-Gal units (8W I think). So just trying to pin down the problem (not really sure what is causing my GH readings other than my own mistakes or bad testing kits).

Do you do top offs? If so, do you do it with RO/DI/Distilled? What is your water change schedule?
I had a tank have very very high dGH and TDS when all I did was top offs with tap water, but after a month of 50% weekly water changes it lined right up with the tap.

Do you have anything in the tank with the higher GH that may be buffering the water? i.e. shells

If you are topping off or doing WCs with the tapwater then the GH will go up because you as the tank water evaporates, the dissolved minerals are becoming more concentrated. Adding new tapwater just adds more minerals so the GH keeps going up. Your plants will use a little of them but for the most part the GH will keep increasing over a long period of time unless the substrate or a high CEC (cation exchange capacity) filter media is used to remove them. Using RO water to top off evaporation keeps you from adding more minerals.

I try to avoid topping off my water, I just do weekly water changes on both tanks. But I think Franco might be up to something...my theory is that I keep adding something with my regular fert. dosage and over time (water use to be at 5 GH initially) it built up to the level that it is now. I have been reducing my dosage of Mg and Ca (just the excess I believe was causing the problem) and my GH has been slowly decreasing and it is now at 10. My plants and fish seem to be doing fine, now that I started paying more attention to fert. details jaja. Thank you for your help!