Did I kill my bio-filter?

[Squall]

I currently have a 40-gallon and a 20-gallon. I had my non-Discus in the 20 and all 4 of my discus in the 40. Recently, 2 of my discus have been through 2 cycles of breeding with no luck. Everytime they lay eggs, I have taken out the one other mature discus and leave the young one in with the pair. The young discus usually stays away from the couple, however, the couple ate the first eggs, let the second batch hatch, but ate the wrigglers. Once they did this, i decided to move my other fish out of the 20, so I could put the pair into the 20. I removed the gravel and inserted 2 sponge filters and left the current HOB on it to seed the sponge filters. I let it run for 2 days and was checking parameters and my ammonia was up to .5 ppm. My ph was at (or below) 6.0. Since my API test kit doesn't test below 6.0, I can't be sure if it got below 5.0 or not.I know this is Ammonium, but for good measures, i even checked nitrites and nitrates. Nitrites were at 0, nitrates were at 10 ppm. I changed half the water (I only have tap water available atm). I checked again this morning, and the ammonia was up to 1.0 ppm.Since there are no fish in it, I did another 40% water change and this time, i didn't put the discus buffer in it, this way I could checked ph. I had brought the ph up to 6.4 but still my ammonia was at .50 ppm. I check 6 hours later and the ammonia is back to 1.0 ppm and the ph is still 6.4...I got no idea what is happening, the ammonia was at 0 before I removed the fish! Makes no sense to me at all. Any ideas what is going on? I am currently sacrificing a platy to see if this is a problem. I will add that I checked the 40 gallon and the ammonia level is 0, so I know the test kit isn't bad.

[Orange Crush]

If you have no fish then no bio waste was being created to feed the BB. BB go bye bye.

[Squall]

Yesterday evening, i added a platy, I swapped a filter from my 40 to my 20 (both are Marineland HOBs and take same filters). This morning, I checked the ph first...it crashed. Bagged platy (still doing fine), did a 75% water change , let it sit for an hour, checked ph, its at 6.6, Ammonia at .25ppm. Swapped out another filter, due to crash, and adding sodium bicarbonate to attempt to raise and stabilize ph. Any other suggestions? Last night, I observed that the filter I had swapped, turned whitish and the tank got slightly cloudy. I have no idea what caused this. I had trouble with this 20 gallon when i first purchased it, and it refused to cycle after 3 months. On the 4th month it cycled completely, and was fine until I cleaned the gravel out, and made it bare-bottomed a few days ago. When I did this, even with fish in it, the ammonia rose and I am having the same trouble again. Ammonia won't go away, with or without fish, and even without fish it won't drop.......so bewildered.

[Orange Crush]

When you removed the gravel a lot of the BB went with it. Your tank is cycling again. This will cause your pH to crash and ammonia/nitrIte to appear. That 1 platy will not create enough waste for BB to be in large enough #s for a fully stocked tank. I would take him out and do a fishless cycle.

[Squall]

I was doing the fishless cycle before the ph crashed. However, it wasn't dropping the ammo. So when I added the platy, it was to check if the tank was safe. After the platy survived over night, I also added our red-tail shark back into there and the 3" angel. The ammo has dropped to zero now that i switched another filter, and i am monitoring the nitrites and nitrates. However, before my precious discus pair go in and these fish move out, I am watching it to make sure. I brought the ph up before adding the other fish, by using the baking soda. This helped a lot. I have begun adding the discus buffer now to drop the ph back down. it contains calcium and maganese and this should hold the ph once it drops back. It will probably take a couple 2-3 days before its safe for the discus. Do I need to do a major water change to clear out the bicarbonate of soda(baking soda)? Or is it safe for the discus?

[Orange Crush]

What is the kH of your water without adding anything to it?