Random Ammonia spike?

Question
Hey Andrew, I actually have a couple questions for you but they all relate to a semi-recent scare with one of my aquariums.  The scare seems to have ended but I want to make sure it stays that way so I'm hoping you can shed some light on the situation for me.
About 2 months ago our well established tank experience a random ammonia spike, it tested at 8ppm!!!  We only even realized the spike because the fish seemed to be having seizures in which they'd dart (not flashing) around the aquarium and run into the glass or the rocks.  The tank had been established for about a year, is 55gal, freshwater, gravel bottom, sandstone rock decor, 2 bubble wands, great filtration, kept at a constant 80deg., changed out 10gals a week and was home to (3) 4 inch severums, (1) 10 inch pleco and (2) green terrors ( 2 inches and 5 inches).  Naturally, we freaked when we realized the ammonia level so we did a large water change (about 20 gallons) and we added Amquel Plus.  Well unfortunately that seemed to make the situation worse because at this point the fish were all gasping for air, the water smelled like sulfur, and the female green terror had a horrible seizure in which she smacked into the glass and floated lifelessly for about 20 seconds.  Over the course of a week or so we used ammo chips (which we replaced every other day) and added ammolock.  The fish still seemed in distress so we added Amquel Plus again and sure enough another fish had a horrible seizure and all of the fish were again gasping for air.  We threw out the Amquel Plus since there seemed to be a correlation with the extreme seizures and lack of oxygen.  For about 2 more weeks we did frequent water changes and continued to use the ammolock and ammochips, but the ammonia level was still testing above 8ppm.  The ammonia tester is the kind were you add 2 different solutions to the water sample and the water turns from yellow (safe) to dark green (deadly).  I assumed the test was accurate since the fish were still having mini seizures and were still not breathing well.  At this point we had to "reorganize" our other aquariums so that we could rescue all the fish from the deadly ammonia tank and place them into another well established tank with no ammonia.  We immediately lost our pleco in the new temporary tank :( but the other fish seemed to be doing well in the ammonia free tank.  While the ammonia filled tank was free of fish I did a 50% water change and continued to use ammochips, but to no avail...after 2-3 more weeks the ammo level was still 8ppm and as if that wasn't bad enough the ammonia level in the temporary tank had now risen to 4ppm despite frequent water changes and infrequent feedings.  Totally fed up at this point, we did a 95% water change in the big empty tank, we added a mixture of freshwater and 10 gallons of water from another healthy tank's gravel.  We also changed the bubble wands out and replaced them with long bubble stones and we added an additional filter, a huge bio-wheel filter, and we added Prime to the water.  Within 3 days the water went down from 4ppm after the huge water change to 0ppm!!!  The tank seems to be stabilized so we added 2 of the fish back today but I'm worried that this may happen again.  Do you have any idea as to why we experienced this apparently random ammonia spike?  If it happens again what should I do?  Also, when I do water changes, should I not suck the gravel?  And how much food should I be feeding these fish?  I doubt I overfed them since they always ate everything I gave them and still acted starving, but maybe I really am feeding too much...

Sorry this is soooooo long, but I'm really worried that another ammonia spike will happen if I can't pinpoint the reason for the first one.  We have 7 aquariums but these particular fish are my favorite and I really want them to live.  ANY input at all would really be appreciated by me and my fish.  Thanks.

Answer
Well I don't care about the long question but the ammonia can just come out of know where and it can become a problem but feed the fish twice a day at the most and do suck the gravel that is important to get any food and debree that is in the gravel but their is really is not any medicine to get rid of ammonia