You need an ammonia tester as soon as possible. Liquid testers are usually more reliable than strip testers. Most of us use the API master test kit.
Fish excrete ammonia, which is poisonous to them. Ammonia eating bacteria will grow in the tank, but it takes a few weeks. Until there are enough of them, ammonia will build up in the water. Once these bacteria start to grow they turn the ammonia into nitrite, which is also poisonous to fish. A second type of bacteria grows in the tank which eats nitrite and turns it into nitrate, but again these second bacteria take a few weeks to grow and until there are enough of them nitrite builds up in the water.
Ammonia appears first. For a few weeks you will have no nitrite, just ammonia. Then nitrite will appear and ammonia will go up slower and slower as more ammonia eating bacteria grow till it stays at zero. But nitrite will continue to go up until the nitrite eaters start to grow, then that too will slow down until it finally stays at zero.
You are doing what is called a fish-in cycle and the way to keep the fish safe is by doing water changes to remove the ammonia, and then the nitrite. Ideally, test every day and do a water change whenever there is a reading above zero for ammonia and/or nitrite.
Other things you can do include:
Feed the fish only once every 3 days. The less food they are fed, the less ammonia they produce. Fish will not come to harm if they are fed once every 3 days.
Get some Tetra Safe Start. This is a bottled bacteria product, the one with the best reputation.
Get some live plants. These use ammonia as fertiliser and will remove a lot of ammonia from the water. Floating plants are very good for this - water sprite, Amazon frogbit, even elodea or hornwort stems floating on the surface.
Fish excrete ammonia, which is poisonous to them. Ammonia eating bacteria will grow in the tank, but it takes a few weeks. Until there are enough of them, ammonia will build up in the water. Once these bacteria start to grow they turn the ammonia into nitrite, which is also poisonous to fish. A second type of bacteria grows in the tank which eats nitrite and turns it into nitrate, but again these second bacteria take a few weeks to grow and until there are enough of them nitrite builds up in the water.
Ammonia appears first. For a few weeks you will have no nitrite, just ammonia. Then nitrite will appear and ammonia will go up slower and slower as more ammonia eating bacteria grow till it stays at zero. But nitrite will continue to go up until the nitrite eaters start to grow, then that too will slow down until it finally stays at zero.
You are doing what is called a fish-in cycle and the way to keep the fish safe is by doing water changes to remove the ammonia, and then the nitrite. Ideally, test every day and do a water change whenever there is a reading above zero for ammonia and/or nitrite.
Other things you can do include:
Feed the fish only once every 3 days. The less food they are fed, the less ammonia they produce. Fish will not come to harm if they are fed once every 3 days.
Get some Tetra Safe Start. This is a bottled bacteria product, the one with the best reputation.
Get some live plants. These use ammonia as fertiliser and will remove a lot of ammonia from the water. Floating plants are very good for this - water sprite, Amazon frogbit, even elodea or hornwort stems floating on the surface.
