Well – old thread or not – if the “noobs” are reading this, I think we can now give a definitive answer to the question.
It will do no harm to use these products, but you shouldn't rely on them to cycle your tank.
Maybe you will find that for you they provide a “quick fix” - maybe they will speed up the natural process – maybe they will do absolutely nothing.
So - the oldest rule in the book still applies …...... go slowly, test often, and be patient.
You have to remember that cycling a tank often takes up to six weeks, and adding more fish just because you can't wait is going to stress out the load the cycle can take. There are no guarantees in a bottle that will negate that.
When your tank is ready, it's ready, and your tank doesn't care what the label on a bottle says about that.
There's no harm in trying this stuff – but like I said – don't rely on it – rely on your test kit instead.
The only fool proof way I have ever found to instantly cycle a tank, is to run an extra filter on an existing tank for a month or so – then fill the new tank, add fish, and add the cycled filter (whilst it's still dripping wet from the original tank it was in).
Gunk from a fish shop is not ideal – it may start things off, but it will not get the filter up to speed straight away, it will still need time to build up (could be a couple of weeks). You also run the risk of transferred disease, snails, other parasites and goodness only knows what else.
In short, for a total newcomer, or to anyone else starting from scratch, there is no easy fast answer.
It's when you don't appreciate that that mistakes happen.
