I am new at aquariums and have got this stuff called "cycle". The directions say that it should be used weekly but someone told me it's only neccessary to use it to start a bilogical filter. Can someone enlighten me?
basically it gives a 'top up' to the beneficial bacteria you have in your filter etc. strictly speaking in and established tank you wouldn't need it because the correct amount of bacteria are present.
however, i tend to use it everytime i clean the filter foam to help replace any bacteria lost in the process and also every now and then when i do a water change 'for luck'.
with a bit of experience you'll soon know by 'gut instinct' whats right for your particular tank.
The tank cycle won't be sped up by adding any bacteria-in-a-bottle. The only thing you need is patience. (And a little household ammonia to start a fishless cycle...)
I will be the first to admit that the idea of bacterial elixirs in a bottle is a good one, in theory... However, I have never seen results from using them.
Just to add another vote in opposition to Cycle...
The stuff is worthless, junk and doesn't do ANYTHING beneficial for your aquarium, in my opinion. Healthy aquariums can be started and maintained without Cycle. Don't waste your money.