random nitrate and amonia spike

so in my tank that has been setup for around 4-5 months for no apparent reason (or that i know of) i get a really high nitrate and and a sign of ammonia. haven't had any deaths before or after but i am afraid that they will come soon i do a water change every week and have only had a small amount of nitrates when i do. No rocks/sand has been moved to create a cycle. what could have caused this and what tips should i do. i am planning on doing a 50% water change right after i post this message hopefully it helps. :fingers:

like is it possible that my tank hasn't cycled like i thought. during the cycle i tested my water weekly until my water tested normal for a month straight. Also if it helps my sand has had a brown diatom algae which started when my nitrates spiked. on my first tank i didn't go through this problem and that was a 29 compared to my current 75?

have you added anything ?? rock, sand, etc ?? if not, it could be a standard case of overfeeding, decaying food = ammonia and nitrates

What are you using for a test kit?

i have changed my lighting and added a bigger protein skimmer i dont understand how those could cause problems with my nitrates or ammonia..also i am using api test kits they are still good ive checked them with my ro salt water before i did the water change and read 0 as it should

overfeeding leaves organic compounds in the tank, these decay, if there isnt enough bacteria established ... there is nothing to consume the nutrients.

Are you running a canister filter? Is there an old bag of carbon in the sump? Any bio-balls, ceramic rings or similar?

i do run carbon but only every other week to polish my water but on the off weeks i take them out. i feed my fish the exact same amount every time i feed my fish. (i use specimen cups and have the same amount in each cup) if i was over feeding wouldn't it be the same every time instead of a random spike like it is now? before setting up my tank ive read through the tank problem page and noticed everything people have done to create nitrates so i try to do the opposite so i dont have this problem. lol, and thanks for all this help

I run carbon all the time. I think it is most effective when you run a couple Tbs of carbon in a mesh bag and replace it every week.