high nitrates - always!!! PLEASE HELP

Hello Everyone

i have a 100 gallon FW. i consistently have high nitrates, which r around 60 ppm, as indicated by my API testing kit.
nitrtitea and ammonia are alway 0.
i have two external biowheel pumps, before that used an UGF. the odd thing is i have a 30 g quarantine tank which contains a biowheel filter as well - no animals or plants. the nitrates are always that high if not higher in there.
in my 100 g i have a small angelfish, a highfin pleco (6"), and a senegal bichir (8"). i added some marimo mossballs and i put katappa leaves and bark in.
I tested the tap water it comes up clean.
does anyone know how to fix this? i dont want to completely change the water every week.
thank u for any input!

i vacuum about once a week, before the water change.
is there a more reliable brand of test kit? the fish r fine. swimming active not gasping eating etc.
i only feed one a day. tried every other day only change i got were upset fish about not being fed. there is no food left in aquarium. except the cucumber slice for a few hrs for pleco.
it almost seems like my nitrate eating bacteria r asleep.

is there such a thing?
what do u recommend?

i am sorry what r photos plants? i thought about plants, guess i will start buckling down and redaing up on plants.

oh my tap nitrate is 0 and the substrate is from substrate source, like a rough sand. (approximately size of cat litter).