Fish in cyclying

[FishSmart]

Hi everyone,
I’m currently doing a fish-in cycle (day 3) in a 20-gallon long with 4 mollies and 1 betta. I’ve kept tanks before and was familiar with cyclinga few years ago. Of course it's been a while and I completely forgot about sponge filters and that they’re often recommended. Is it too late to switch to a sponge filter now, or would that cause more harm than good at this point?

Behavior-wise, 2 of the mollies sometimes rest on the substrate/decor, then get up and swim around, explore plants/rocks, and settle again. They’re not gasping, still eating, and the other 2 mollies + betta seem fine. I know this can indicate stress, especially in a new tank. Anything I can do for them?
I did a partial water change today, added Prime, and plan to re-test in the morning.
I’m very open to all criticism and learning!

Thanks in advance!

 

[Andy Sager]

Hi everyone,
I’m currently doing a fish-in cycle (day 3) in a 20-gallon long with 4 mollies and 1 betta. I’ve kept tanks before and was familiar with cyclinga few years ago. Of course it's been a while and I completely forgot about sponge filters and that they’re often recommended. Is it too late to switch to a sponge filter now, or would that cause more harm than good at this point?

Behavior-wise, 2 of the mollies sometimes rest on the substrate/decor, then get up and swim around, explore plants/rocks, and settle again. They’re not gasping, still eating, and the other 2 mollies + betta seem fine. I know this can indicate stress, especially in a new tank. Anything I can do for them?
I did a partial water change today, added Prime, and plan to re-test in the morning.
I’m very open to all criticism and learning!

Thanks in advance!

It doesn't matter what kind of filter you use because the nitrifying microbes will adhere to wherever there is the most amount of oxygenated water in the tank, filter, sump, canister, etc. If you are using a HOB filter, that will usually be in the filter floss or cartridge or sponges in the box. The amount of microbes will all depend on how much ammonia production is happening from your fish so even if you had a huge sponge in your filter but had a small ammonia amount in the water, it would only have a little microbe bed to consume and convert that little amount of ammonia.
As for your fish not doing well in new water, there are a few possibilities. 1) Mollies generally like hard alkaline water. Do you know the GH ( General Hardness) of your water? If it's too soft, that can effect the fish's behavior.
2) What is the M/F ratio of your mollies? It should be 1 male per 2-3 females OR they should all be males with no females. If there is even 1 female amongst 3 males, the males will fight with each other for breeding rights which could be that you have 2 losers in battle hiding at the bottom.
3) The fish were sick when you got them.

So once you figure out if it's #1 or# 2, then we can discuss potential medications after you list your water's parameters ( pH, & GH).

Hope this helps.