Low Ammonia & Nitrite levels

Question
QUESTION: I have a 15 Gallon Hexagon Tank
stocked with 8 Neon tetras, 3 Guppies, 2 Glo fish, 2 Catfish and one Dwarf frog. I use a Marineland water filter with a Bio Wheel  and also have a Bio block in my tank.
I have been setup since June 1st, I let my tank run through the cycle process which took a while and all levels seemed to level off added more fish and the tank was running fine until about three weeks ago I  changed the water filter as called for did a partial water change and my ammonia levels started to rise along with my Nitrite levels.
After many partial water changes, and use of Stress Zyme, Amquel plus the levels go to zero then begin to rise again.
What did I do wrong??

ANSWER: I would guess that it was your filter.

Your filter holds much of your beneficial bacteria, and the gravel holds the rest. Cleaning out too much of the filter and/or too much of the gravel can cause the tank to mini-cycle. Clean small amounts at a time.

However, if you are showing nitrites the cycle is likely almost complete. So there should be no worries.

Also, careful with the dwarf frog. Then can nip a guppy's flowing caudal fin right off.

-Nick

---------- FOLLOW-UP ----------

QUESTION: Thanks so much for your quick response to my question, but with a carbon filter and bio wheel should I not change my filter every four weeks? I was told by pet store personal to just rinse filter in tank water when doing weekly water changes and re use the filter until it is basically falling apart. should I rinse the Bio wheel also? Is this good practice? I just don't want to offset the beneficial bacteria that is built up, Its hard to not change some of the filter media without destroying the bacteria colonies.
Any thoughts? advice?
Thanks a million Nick!!

Answer
Normally, with an established tank you can do this no problem, but with your new tank you have to do less until the filter fully establishes.

Change the carbon once a month, but when you are changing the carbon do not do a water change at the same time.

Same with the Bio-Wheel. Rinse it every couple months in tank water, but do not do a water change or change the carbon at the same time.

The trick is to spread everything out so there is always a good population of beneficial bacteria somewhere in the tank.