My tank is 1 year and 8 months old and its fully cycled and i dose estimative index
8 ppm KN03 nitrate 3x a week
2 ppm KH2P04 phosphate 3x a week
2 ppm K2SO4 Potassium 3x a week
30ml seachem flourish 3x a week
40% water change each week+1 teaspoon seachem Equilibrium
And i clean my filters 1 a month under tab water. Filters eheim Pro 3 2075 and Eheim Classic 2217
Cleaning the filter under tap water could be doing it if you're cleaning all your media at once for both filters. Although contray to belief, bacteria is more resistant to a tap water washing than people make it out, if your water company does heavily chlorinate, it could be killing off some of your bacteria. If you want to keep using tap water, stagger your filter cleaning, so 1 is always running and even if you kill off most of the bacteria washing one, the second one can still keep filtering fine and will help build the one you cleaned back up in a few days, then do the other one next month/2 weeks later. In a year and 8 months you shouldn't have ammonia/nitrites unless by doing both filters at once, you are causing a mini-cycle each time.
I usually always wash my sponges in tap water from my shower head. I can't get them clean just rinsing them in some tank water, especially from my turtle tank. Those things get caked with mulm.