biological filtration....

Can anyone tell me what would be happening..........
My tank has been setup approx. 3 1/2yrs. now. My water quality has
always been excellent. I do water changes (not as often as I should), but I do do them. My tank was at 0 ammonia, 0 nitrites and 5 nitrates for years..... why am I all of a sudden showing traces of ammonia (between .5 and 1) and nitrite = 0, nitrates = ~ 5. It's been like this for over 1 month now.
How can you see traces of ammonia with no nitrites?
My tap water seems to be around .25 ammonia

pH = 6.0

wataugachicken said:

if it's the tank you listed in your signature (planted 120), have any plants been dying? rotting plants put a triple whammy on water parameters:

plants stop taking up ammonia
plants produce ammonia through decay
plants replace bacterial filtration to an extent, so when a plant is lost, the bacteria is not there immediately to cover the slack.

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Actually, I did a major "pruning", must of been hundreds of dollars of plants I took out......seemed like it anyways. It was a garbage bag full.
I only left a few that I wanted and that is when I noticed the "spike".
I guess that is what happened. I didn't even think that that would make a difference on ammonia levels. oops. Anyways, I went out today and got some more plants (different species).
To answer the WC question,.........sometimes I go 2 months without a WC and sometimes it's every 2 weeks. I don't have a cover on the tank and it evaporates at a rate of 3L per day so I replenish 6L of fresh water every 2nd day. I try to vacuum /WC at least every couple weeks but sometimes it just doesn't happen, especially with a 2yr old around that LOVES to help out! LOL

Thanks for all your responses!

Slappy*McFish said:

Do you get these readings right after a water change?

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No. It's been approx. 2 weeks since the last WC and I tested yesterday.

Hooked Newbie said:

Are you missing any fish mysteriously?

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no. all is accounted for. I know rotting fish really spike up the ammonia levels