I know of 1 product that can help at times like this, but I warn, it's not going to be real cheap. The product is called polyfilter, most LFS's have never even heard of it, but its the one thing that can perform wonders almost overnight. In your case, it could be the only chance they have. Be prepared to order this online, you can find it at Dr's Foster & Smith here: http://www.drsfostersmith.com/produc...olyfilter&Np=1
I would suggest getting the large one, you're going to need it, and I know they have overnight delivery available. In the mean time, 30% water changes every day.... stop feeding them, get as much carbon in the filter as possible, and lots of decorations so they can hide, this will help a lot with stress. Whatever's in there now, add more... a lot more.
I can explain to you what happened, as I've seen this before and is what I often warn about when using products like BioSpira.
When your power went out, waste built up in there, ammonia levels spiked. This went on for 2 days, you were probably even still feeding the fish... BioSpira is a liquid form of nitrifying bacteria, meant to break down waste quickly. What many people don't know is that you can actually kill the bacteria if the ammonia level is too high. The directions on the packaging always say to add it when you add the fish. What they don't add, which I think is crappy of them, is that if you wait too long after adding fish, the bacteria die from too much ammonia, and further spike the ammonia levels in the tank, causing a highly toxic mess. Your fish would be safer in a brand new set up working through a normal cycle that you can control. Outside of acclimating them into that as if they were coming home from the store, the polyfilter is the only thing I know of powerful enough to help you here.
The reason I suggest getting the biggest one is so that you can use it to help you get through an easy cycle, because even once the waste is absorbed, that tank will still have to cycle. If you want to use a bacteria starter, the safest one I know of is Biozyme, and it's possible that Foster's & Smith has that too. Considering you currently have nitrites going, I would say you have a good start on the cycle already, we just need to ease it up for the fish. The filter media will suck almost everything out of the water for pollutants without touching your bacteria colony. The trick in this method is with water testing and knowing when to take the media out and put it back in.
To start, cut 4 pieces to fit into the back of your filter. If it means removing the cartridge, do that, but lay the cartridge in the tank to preserve bacteria. Insert the 4 pieces into your filter after your 30% water change, and do not feed the tank that night. Turn the lights off and let it do its thing. The pads will turn yellowish brown to green brown in color, this is good, do not throw them away yet. This is what the pads is pulling out of the water, leave them in for a full 24 hrs. After 24 hrs replace those 4 pads with 2 fresh ones and the original filter cartridges, then do your water testing. It might take up to 48 hours to see a big difference, but polyfilter tends to show results in 24. Continue replacing the 2 pieces of polyfilter every 1 - 2 days as it discolors and shows that it is needed. Test your water daily, keep track of your results. Once your ammonia and nitrite are both at 0, remove the polyfilter pads. Continue testing your water every 1 - 2 days, watching for a nitrate level to finally appear. If ammonia and nitrite spike too high again, it's ok to use a piece of polyfilter, but limit yourself to 1 pad. The bacteria needs some waste in order to grow and thrive and reseed the tank. While using the polyfilter always do water changes before inserting a new piece, and keep the water changes small. You don't want to remove any bacteria that are starting to grow in there, which would slow down your cycle. The polyfilter may allow you to get by without any water changes during your cycle, which would be great.
Best of luck to you, if you need more help, please ask!