Fast Cycling?

With some nitrite testers the reading can show zero if the actual level is off the top of the scale. Can I suggest you dilute a sample of tank water about 1 in 10 and retest. If it's still zero then you are OK, but if it shows a reading other than zero, the tank water has a nitrite level so high the tester can't cope.

Your nitrate was lower on day 4 than the first day. If you have filter bacteria making nitrate it should be higher. Have you been doing water changes as they would lower it? And on the subject of nitrate, if yours is a liquid reagent test kit, all brands need one bottle to be shaken very well each time you use it - are you shaking it?

One thing that does worry me is that you say your levels remained high then reduced. You should have been doing a water change whenever you had a reading for ammonia and/or nitrite above 0.25. Levels higher than this can kill fish outright and weaken their imune systems if they survive making them more prone to disease.



One thing I'm curious about - what exactly was in the bag of water the shop gave you? Because the filter bacteria don't live free floating in the water, old tank water is virtually uselss for cycling. But did they add something to the water?

You'll find it is a common belief that the filter won't cycle unless the levels are high. This is not true. In fact water changes are regarded as necessary when there are fish in the tank and the levels are high. The bacteria don't live in the water, they grow tightly bound to surfaces so changing water won't stop them growing, unless you don't add dechlorinator in which case the chlorine in the new water could kill them. And they don't need high levels to get them to grow. Our test kits can't measure trace amounts, and trace amounts are enough to get the bacteria to multiply. One way to look at is - it doesn't matter if the bacteria are ankle deep or over their heads in food, so long as there is even a tiny bit more food than the ones already there can eat, they'll multiply.

Keep an eye on your levels for another week, and if ammonia and nitrite stay at zero, the filter will be cycled. But you'll only have enough bacteria to eat the waste from the fish you have now. When you add more fish, there will be more waste and you'll have to grow more bacteria to deal with this extra waste. As a general rule of thumb, it is safe to add in one go up to one third of the amount of fish already there. Keep an eye on the ammonia and nitrite levels after you add new fish, and hopefully they will stay at zero. If not, do water changes to get them to zero. When you've had a week of zero, you can get more fish. Again it's a third of the the total fish (the first ones plus the last additions). Keep on like this, a few at a time, till you have all your fish.

Have you found the community creator on this site? It is a useful tool for working out how many fish you can have, though it is a bit overgenerous so don't get as many fish as it says you can have. You'll find the CC in the fish profiles (menu at top of page). Just click on a ny fish and you'll find the CC at the bottom of the page. Fill in your tank details and add fish. You do have to register separately from the forum to save your data.