Ariel ... please please please ... don't throw sponges away unless they are falling to pieces. Just clean them lightly in some old tank water and pop them back into your filter. This will be why you have Nitrite in your tank. Everytime you throw a sponge away because it's dirty you put your tank back into cycling from the beginning. The filter manufacturers tell us to change sponges every 3 months (or what ever, depend on the company) ... this is purely to make more money from you. It is not for the good of your tank or fish.
Now, bottled bacteria. Well there's been several arguements over the years over whether there is anything in those bottles or whether they are just another money making scheme. I've tried a few myself - API Stresscoat, King British Safe Water being the two I can remember the names of. I've found them to be of very little help and now I've stopped wasting my money on them.
I've found the best way to keep the tank ticking over is to get as much sponge media in the filter as you can and only clean it when the flow from the filter slows down significantly. All I do then is rub the sponges in dirty tank water and put them back. I've not bought new sponges in over 3 years.
I hope that helps you get this nitrite under control
Now, bottled bacteria. Well there's been several arguements over the years over whether there is anything in those bottles or whether they are just another money making scheme. I've tried a few myself - API Stresscoat, King British Safe Water being the two I can remember the names of. I've found them to be of very little help and now I've stopped wasting my money on them.
I've found the best way to keep the tank ticking over is to get as much sponge media in the filter as you can and only clean it when the flow from the filter slows down significantly. All I do then is rub the sponges in dirty tank water and put them back. I've not bought new sponges in over 3 years.
I hope that helps you get this nitrite under control