2 Guppies in 3.5 gallon tank

[Essjay]

Can you move the whole filter to the new tank? Most filters suitable for 3.5 gallons are also suitable for 5 gallons.

 

[mcordelia]

In glad things are starting to make sense! Yes, I would run both filters at the same time for at least the next 3 weeks. Did you end up moving Rainbow already? Can you test your ammonia in the 5g the day after you move him? (If you moved him yesterday, test the ammonia at some point today and let us know what the reading is )

@essjay I suspect that if this is a typical kit tank they way I have seen them in the pet stores around here the hood cutout may not be sized correctly to accommodate the other filter, so running the "dedicated" 5g filter in the back and running this in the front of the tank may be the best way to transfer the bacteria from one filter to the other, in terms of getting the pieces to fit together properly. What are your thoughts?

 

[Essjay]

I'm used to my internal filters which contain sponges Those are easy to swap from one tank to another as they have just a wire going through the lid.

If there is any way to make the filter media from the 3.5 gall's filter to fit inside the 5's filter, that's the best way. Though I expect the media is carbon cartridges - that seems to be the case in small filters and HOBs. If this is the case, they won't fit another filter.
Running 2 filters in a 5 gallon tank won't leave much room for the guppy though.
If the filters do have only carbon cartridges, another option might be to cut a hole in the cartridge and empty out the carbon, then cut the bag part off the frame and squeeze that into the 5 gallon's filter. Not ideal but better than nothing.

 

[Ratchet4x4]

In glad things are starting to make sense! Yes, I would run both filters at the same time for at least the next 3 weeks. Did you end up moving Rainbow already? Can you test your ammonia in the 5g the day after you move him? (If you moved him yesterday, test the ammonia at some point today and let us know what the reading is )

@essjay I suspect that if this is a typical kit tank they way I have seen them in the pet stores around here the hood cutout may not be sized correctly to accommodate the other filter, so running the "dedicated" 5g filter in the back and running this in the front of the tank may be the best way to transfer the bacteria from one filter to the other, in terms of getting the pieces to fit together properly. What are your thoughts?

Thank you guys. I did move rainbow over on the 2nd. I moved part of the gravel also. I also took more of the old water from the 3.5 gallon tank and I stuck the old 3.5 g filter in the new tank Also. No the filter in 5 gallon tank is much bigger and looks like it’s better quality. I’ve added a bigger flat heater also. Rainbow is fast like Sonic the hedgehog now. im afraid to make any changes as tomorrow I plan on ding water change. When can I add another fish?

 

[mcordelia]

I would give it 3-4 weeks for the beneficial bacteria to establish itself in the new tank, at which point you can remove the filter that was in the 3.5 gallon from the tank. When you add a new fish, I suggest you use a product called tetra safe start, or Dr Tim's beneficial bacteria (it's got a slightly different name on the box), to introduce more good bacteria so that there is no ammonia spike when the new fish is introduced.

I'm glad that the move went well! Keep testing for ammonia and nitrites every day for the next week, though with one fish you probably won't see any which is good.

I think your plan on waiting a day before doing the water change is a good one,that way Rainbow does not get stressed

What an exciting upgrade!!! If you want to add more things to your aquarium before you get new fish, consider live plants! Rainbow would probably really like it, and there are varieties that are good for beginners like hornwort, anubias, java fern, java moss, amazon sword, and some cryptocoryne.

Good luck!!