If you just add water to compensate for water evaporation salts and minerals will buildup over time and eventually kill everything in your tank. Plants and fish. A good natural example of this is mono Lake
Currently the only things that can live n the water are brine flies, brine shrimp. and algae . Eventually the future nothing will be able to live in its water.
So you need to do water changes to remove the bade stuff in the water. Also tap water adds minerals like Calcium, magnesium, boron, zinc, copper, and nickel. Most fertilizers either don't have these plant nutrients or the fertilizer just don't have enough. Just occasionally adding water results in plant using up all the nutrients in the water that are not in your fertilizer. So the plants will not grow most of the time.
Many people monitor the water harness (GH test) to insure that the water conditions are stable. You should do this to insure the waterGH stays consistent with your well water hardness. The GH test primarily detect only Calcium and magnesium. You Should also monitor your water alkalinity (carbonate levels (KH). and water PH. The goal is to a water change schedule and to keep these parameters stable.
Nutrients in the water (Calcium, magnesium, phosphate and boron) can .react with each other resulting in nutrient shoartages. PH and KH can also insteract with the sulfate nutrients in the fertertize and the iron ingredient. These can also result in nutrient shortages. If your PH less than 6.5 and KH is zero most fertilizers will work and you likely would only need to fertilize once every water change. But it can be diffiult to maintain zero kH and a low PH.
EI fertilizer dosing works for many people mainly because nutrients are dosed almost daily. The main problem people have with EI dosing is that not all fertilizers include all Nutrients resulting in nutrient deficiencies. Also most fertilizers use iron gluconate which only lasts few days or Iron EDTA with is only usable in water with a PH 6.5 or less. Iron DTPA is the best iron ingredient since it is stable up to a PH of 7.5 and maybe even be stable up to a PH of 8. Many people state CO2 is the most common deficiency but that statement is wrong. CO2 changes water PH and since most EI fertilizers have Iron EDTA keeping CO2 levels high is needed to Keep PH low enough for the fertilizer to work.
In your case you want to use a fertilizer with no nitrogen and no phosphate since you know your water has these. Probably the best commercially available fertilizer for you is GLA EDTA+DTPA micro fertilizer
. This is them most commonly used EI micro fertilizer with Iron DTPA added to allow it to be used at the higher PH of most tap water. If your water has a low GH you might need to also add a GH booster. Or you can used the fertilizer your have but dose them more frequently.
You need to work out a fertilizer and water change routing that works for you. With all your fish you might be able to get by with less frequent water changes and and a lower overall fertilizer dose. But the only way to do that is to experiment until you find a water change method and fertilizer dose that works for your.