How long should I wait to put seeded Bio Media in QT tank before adding fish?


how long should I put seeded bio media in my QT tank for new fish? I don't want to do it to early and cause a cycle, or too late and have an issue.

Whats your thought?


All I can say is what I do that works for me.
With multiple tanks and spare tanks sitting around and an addiction to getting more fish.

I am at this moment sitting outside a LFS that has nothing at all that is of interest. If however I saw something that was on the shopping list I would buy it and take it home .
An empty dry tank would get the dirtiest sponge filter I could find a dirty old terracotta pot plant some wood snails shrimp and leaf litter. Fresh water and the fish go straight in. ( after aclimating)

The sponge filter is stolen from a tank that has 5 or 6 and replaced with a fresh sponge.
The new tank is cycled enough for a couple of fish with one filter , but perhaps not for a school of 15 fish?
As I am watching the new fish daily they would get a water change or two in the first week. It’s unlikely I would even test the water to be honest. You could test for ammonia just in case.

Should I sell a tank load of fish and have an empty tank the filter would be returned to any tank that has fish. IMO the filter would still be ok 4 or 5 days later in an wet but empty tank but I would not wait any longer in an ( fishless) empty tank.

IMO seeded media is seeded media . A sponge filter is treated just like ceramic media.
I have ceramic media in box filters and would add the whole box filter to a tank that is going to stay running for more than a few weeks or if the new fish were a school of 15.

To answer your question as best as I understand what you are asking.

To early.
You can set a tank up the day before or a few hours before but not more than a few days if you are not going to provide an ammonia source ( poop) to continue to feed ALL the bacteria.

To late.
The fish need a cycled filter within a few hours. Even waiting over night is not acceptable practice for me. The fish get a filter as soon as possible,even if that means a late night on club auction day.

No advantage is gained by adding the filter before the fish are added. IMO.

Personal opinion.
A dirty chunk of foam or floss added to any filter gives me more confidences that old but clean looking ceramic media.
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Add the filter media with the fish if your tap water is ammonia and nitrite free. If its not add the filter media that morning before you buy your fish.


Good point, thank you smee82,
I forgot about people that have ammonia or nitrites in their tap water.
A classic example of how each of us faces different challenges because of the different tap water we have.
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