Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish and plants are just fine with water moving as much as 10 times the tank volume per hour, so a 55 gallon tank with something in the neighborhood of 550 gph is not a problem.
More surface movement can allow CO2 to off gas, but only if you are adding it. If you are not adding CO2, then surface movement generally replaces the CO2 as the plants use it.
The filter media itself does not remove fertilizers. Even activated carbon does not, with one minor exception. AC can remove chelated iron, but only for the first few days when the carbon is fresh. After that the iron remains available to the plants. While many people with planted tanks do not bother with carbon, some do keep it in the filter, where is does not hurt things.
Excess water movement can tear up the leaves. Plants directly in the flow of the filter will not do so well, but there are exceptions. The Bolbitis fern thrives in such a location.
A spray bar can be modified so the blast of water is not quite so strong. You can drill more holes, or enlarge the existing holes, or alter it in other ways to make a gentler flow while still using that much flow overall. Or, as you note, turn down the overall flow with the controls on the filter.
Remember, also that the flow will change as the filter fills with debris.