Nitrite poisoning???

Ok guys so this morning I woke up to find everyone of my fish at the top of my tank...gasping, naturally did a water test and came out at
0 amm
0.5 nitrite
10 nitrate
I dosed with prime as I was straight out to work.
When I came home no change I did a very large water change and the nitrites are 0 now. My rummy nose tetra have perked up a little but most of the other fish are still at the top. I was just wondering how long would it take to see an improvement should they stop gasping as soon as I have 0 nitrites and fresh water.
Or does it take time.
200L
2 bristlenose pleco
7 dwarf neon rainbows
3 platys
3 dalmatian mollies
11 rummynose tetra
2 honey gourami
My tank has been set up since february the only reason this has happened is I had a brain fart the other day and took a piece of filter foam out to seed a new tank only a small piece and forgot that it had only been a few days since I added my new rainbows and the bb had obvs not caught up yet.
Cheers guys.

 

They might just need time to recover from nitrite levels. I'd dose Prime daily until your BB catches up and do water changes like today if you see it rise. What's the temp of the tank? Do you have enough surface agitation?

 

I am running a large bubble disl in one corner and a standard airstone on the other with my pump turned right up, I also have a venturI on my filter working and have left the hood off the tank.

 

Ok now my rummys have whitespot

 

Sorry to hear that. I would use the heat method to treat. Here's more info:

https://www.fishlore.com/aquariumfishforum/threads/ich-ick-life-cycle-and-natural-treatment.153206/