Will it crash my cycle if...

[Karen B.]

Greetings!

I currently have a 20 gallons, cycled since july. Until yesterday, its population was 12 White Cloud Mountain Minnows, 1 dwarf crayfish and 1 snail. 3 days ago, I removed all the plastic plants and planted live one. Running a HOB filter Aqueon quietflow 20 with a prefilter sponge and a medium filter sponge from Aquarium coop.

 

I no longer have the minnows (gave them) and I will get false julii corydoras so I need to change my gravel substrate to sand in about a week. Will it crash my cycle or can I add my 6 corydoras the next day?

 

I alsi bought a fluval flex 15 gallons yesterday and will transfert the gravel substrate in it and some of the driftwood/plastic decors from the 20 gallons (everything will stay in water until the last minute). Can I consider my 15 gallons immediately cycled and add fishes the next day?

 

It’s not that I am impatient but as we are in lockdown, I want to make as little trip as possible to my LFS. 

 

Thank you!

[gardenman]

In the case of the twenty gallon tank, you should be fine. Bacteria live all through your tank, not just in the gravel. The two sponges should house more than enough bacteria for six Corys. (Just a note, Corys and crawfish don't always do well together.) The fifteen gallon is a little trickier. For light stocking I would think you'd be okay. I'd keep an eye on the level though. If you see ammonia starting to spike, then moving your sponge filter to the fifteen gallon tank for a bit should help with that. I wouldn't throw a lot of fish in the fifteen right away, but with light stocking you should be okay.

[Jack.of.all.aquariums]

In my experience the substrate doesn't make a difference for cories. If you want sand though I would just slowly change it out doing like 1/4 of it at a time. 

[Karen B.]

4 minutes ago, gardenman said:

In the case of the twenty gallon tank, you should be fine. Bacteria live all through your tank, not just in the gravel. The two sponges should house more than enough bacteria for six Corys. (Just a note, Corys and crawfish don't always do well together.) The fifteen gallon is a little trickier. For light stocking I would think you'd be okay. I'd keep an eye on the level though. If you see ammonia starting to spike, then moving your sponge filter to the fifteen gallon tank for a bit should help with that. I wouldn't throw a lot of fish in the fifteen right away, but with light stocking you should be okay.

Thank you so much for your answer!

I actually bought the 15 gallons for the crayfish because I wanted corydoras in the 20 gallons. That’s 1 spoiled crayfish I tell you! 🤪

[Dandy Pearl]

I agree with @Jack.of.all.aquariums.@Jack.of.all.aquariums. you can keep the media where it is if you like it. If you still want to swap it, keep the gravel submerged in tank water when you make the move to keep the bacteria alive. Don't rinse it when making the transfer.

Good luck with your tanks!