What you are experiencing is very common. Your aquarium is still not 'mature', which means the filtration system has yet
to establish a level of beneficial bacteria that are capable of consuming the nitrite in your tank. There are no 'set in
stone' rules on how long it will take your aquarium to mature as there are so many factors that affect it. You can help the
process by doing the following
✔ Manually lower the nitrite in aquarium by performing a weekly, 25% water change, to take the strain off your
filter while it matures. Remember to add a de-chlorinator to the tap water.
✔ Use a gravel cleaner to get more waste out of the aquarium.
✔ Feed only small amounts of food every other day until the filter has matured.
✔ Do not add any more fish until the filter has matured.
✔ Remember: Nitrite affects a fish's blood's ability to carry oxygen, so make extra effort to ensure the aquarium
is well aerated.
The 'brown powder' is diatoms in the water taking advantage of the conditions. You should find that they settle down
once your aquarium matures.