Adding a new filter to a fully cycled tank

[Foxy]

I've got a bit of a filter surplus at the moment, having recently merged two tanks into one. I'm in the process of finalizing the configuration for the remaining tank's filtration system. Given that I've got a few filters to spare, I like to keep one running as a backup in case of emergencies or if I need to set up another isolation tank. I've figured out which two filters will work best for the new tank, and I'm planning to store the third one (my U4 filter) for now. If I ever need to bring this mothballed filter online and put it in an established, cycled tank alongside another fully cycled filter, how long would it take before it's considered fully cycled and capable of running solo?

[sSjey]

Adding a third filter to the tank won't increase the overall bacterial population, it will just redistribute the existing numbers. The amount of bacteria in each filter will depend on various factors, such as the type and amount of media in each one.

It's likely to take a couple of months for the mothballed filter to become fully cycled, but even then, it won't be able to handle the same bioload as the current tank. Assuming the three filters have similar media capacity, each one will likely be able to support the waste from about a third of the fish in the current tank. This would be suitable for a quarantine setup with a few more fish, but not for setting up another tank with the same number of fish you have now.

[Foxy]

I'm going to put the tank combining and filter mothballing plans to one side for now and focus on the current setup. I've got a 150l tank with a U4 filter that's rated for 130-240l of water, and I've also got a U3 filter running as a supplement, which is designed to handle 90-150l. I thought that if the U4 failed, I'd be okay with the U3 taking over, although it wouldn't be ideal in the long run since it would be at the top of its capacity. But if I understand the situation correctly, if the U4 were to stop working, the U3 wouldn't have enough bacteria to support the current fish population. This means I'm probably wasting my time and electricity running the supplementary U3, and I should consider mothballing it instead. In the event the U4 fails, would it make more sense to take the media out of the U4 and put it into the mothballed U3 filter? I hope I'm not being too dense here.

[sidthy]

I've got a bit of a filter surplus at the moment, having recently merged two tanks into one. I'm in the process of finalizing the configuration for the remaining tank's filtration system. Given that I've got a few filters to spare, I like to keep one running as a backup in case of emergencies or if I need to set up another isolation tank. I've figured out which two filters will work best for the new tank, and I'm planning to store the third one (my U4 filter) for now. If I ever need to bring this mothballed filter online and put it in an established, cycled tank alongside another fully cycled filter, how long would it take before it's considered fully cycled and capable of running solo?

Not being thick at all, you've got it spot on. This is exactly the approach you should take. If the U4 were to fail, it's best to transfer the media into the mothballed U3 filter rather than relying on the supplementary U3 to handle the full load.

[Foxy]

Thanks for clarifying things for me. I've only got one small plant in the tank, and to be honest, it's on its way out - I've never had much luck with live plants, so I won't be replacing it when it finally gives up the ghost. I've now completed the transfer of the 10 fish into the larger tank, which already had 5 fish, and I've sorted out the filter configuration. Just out of curiosity, I was wondering - the box that contains the bio max media in the now spare unused filter, would the bacteria in that stay viable if I were to just leave it in the tank, say behind an ornament, just sitting there, doing its thing?

[sidthy]

Without the constant flow of water providing it with food and oxygen, the bacteria in that bio max media will slowly perish.