How often to change cartridge & what builds up in tank water?

Question
I have a Tetra Internal Whisper Power Filter.  The instructions for the cartridges I buy don't say when to change them.  A pet store guy told me every three months, and that some people change it every month.

How often do you think it's okay to change the cartridge?  I change it every month, even though the cartridge isn't dirty.  Also, on an Internet site someone was talking about something building up if you don't change the water in a tank.  They either said nitrates or nitrites.  I think they said it causes fin and tail rot, and I think other diseases.

Do you know what they may have been talking about?  What other things build up if you don't clean out a tank or don't clean out a tank enough?  I emailed them but it looks like they don't answer emails.  Thanks.

Answer
Hi Dipan,

Yes I do know what they are talking about and I quite agree.

Some filters even come with things that tell you when to change them, and those are off also.

Your filter needs changed monthly.  You are doing it correctly.

Pet store personnel are often incorrect in their advice, because they are not experts, but are instead, employees repeating what they were told.

Ammonia, Nitrates, Nitrites and bacteria build up if the filter is not changed as often as possible.

I hope this helps you out, Dipan.

:) Happy fish-keeping.  You are doing it right by changing the filter cartridges monthly.

Renee