Do I need to cycle tank again

[deanmarine]

Hi, just after some advice here
I have a 20 gallon nano fish only which unfortunately was overrun with whitespot around 3 months ago. It has since been running with no fish, only hermit crabs. Now, before I add new fish again will I need to complete the nitrogen cycle again? Since there has been no waste in the aquarium I assume that the process need to be repeated even though the same filter components, rock and water are in the tank?

Would much appreciate anyone's advice on this.

Thanks

[Benny314]

So what have the hermits been living on? They'll produce waste too.

As ever restock slowly as you'll cause a spike adding lots at once and the LR and other media won't be able to process it fast enough straight out of the gate.

The bacteria won't die completely off, but the levels do fluctuate depending on bio load so you can crash a system quite easily adding lots of load at once.

[Azedenkae]

Test your filtration capacity and you'll know if it'd be fine to add fish.

[seabass]

As Benny wrote, the bacteria populations have adjusted to the new, lower bio-load. You just have to add livestock slowly, like you did after your tank established its nitrogen cycle.

[deanmarine]

Thanks for the answers, would there be any harm in feeding some small amounts of food and testing to see if there is an ammonia spike to ensure that the cycle isn't going to restart. Or using that as a method to build up the bacteria a bit before adding fish again?

[seabass]

Adding food will add phosphate and build up nitrate. Sure, it will build up the biofilter some, but there is no need if you add livestock slowly (which is the safest method).

[Azedenkae]

Thanks for the answers, would there be any harm in feeding some small amounts of food and testing to see if there is an ammonia spike to ensure that the cycle isn't going to restart. Or using that as a method to build up the bacteria a bit before adding fish again?

That is a good way to test it. That is exactly how I do it.