Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If you removed the media from your bio filter and threw it away that is where your bacteria were.
Now you add new media, and it does not have bacteria yet.
Roughly half the nitrifying bacteria live in the filter (all the media, not just special media for bacteria) and roughly half live on all the other surfaces in the tank.
By tossing the media, you have lost about half or so of your bacteria. The plants and the remaining bacteria are working as hard as they can to make up for this.
The plants are grabbing all the nitrogen they can in any form (ammonia, no2, no3) and the remaining bacteria are grabbing all the ammonia and nitrite they can.
But it is not enough.
Here is what I would do:
~Improve conditions for the plants: better light, CO2, make up for any missing nutrients
~Add more plants, especially fast growing ones.
~Stop feeding the fish. When you resume, half as much, half as often, then a little more as the bacteria and plants catch up.
~If the problem goes on more than 48 hours, or the ammonia or nitrite keep trying to spike, then go buy more bacteria. Read the label and only buy a product with Nitrospira species of bacteria.
~Keep up with water changes to keep the ammonia under .25 ppm and the nitrite under 1 ppm (for fish- I do not know the level for shrimp). Add sodium chloride (salt) when the test results show any nitrite. The dose is 1 teaspoon per 20 gallons. Again, this is fish and plant- safe. I do not know about shrimp.