Mollies Freaking Out & Water Parameters Out of Whack!! HELP!!

Question
A few weeks ago, I transferred my mollies to a bigger tank because they had bred themselves out of their old 20 gal.  I used the 2 hanging filters from their old tank (did NOT change media or clean anything), 75% of the old water, all of the plants, rocks, caves and gravel went into the new tank.  It's an Eclipse system (the new one) and because I was concerned about cycling a new filter, I have yet to put the canopy/filter/lighting on the new tank.  Instead I am using the old lighting along with the old filters (I have always over filtered my tanks so these two should be able to filter a 80 gal tank without any problems).

My mollie tank is always overstocked because they keep breeding faster than I can give them away, but I have learned to do at least 2 partial water changes weekly to help accommodate the overstock issue.  Until now (had them 2 years), I have not had a fish loss.  I also vacuum the gravel approx 20% with each water change and I change filter media once a month, but alternate filters and do not change the media on same day as water change.  i rinse the filter floss in a small bucket of tank water (no more than 1/2 gal in bucket) so I do not kill the bacteria.

A few days ago, I lost a 3 wk old baby.  I chalked it up to nature and didn't think about it again until an adult died the next day (she had just had fry so I figured she had been weak and the others had probably picked on her till she died...it's happened before so again, I chalked it up to nature).  

Then all of a sudden a young mystery snail hasn't moved in several hours, so I pull it out and see it's dead.  Strange....until I see a Tiger Snail is dead too!!!  I remove it and go searching for other casualties.  I don't find any.  But I figure i had better test the water, because i have no idea how long either of the snails had been dead, for sure.

Then I notice that several of my mollies are swimming vertically for a few moments, and then back to normal.  Strange!!! But also concerning!  I look for outward signs of illness, nothing outside of behavior.

Well, my water parameters were off the charts!!! My ammonia was .25 ppm, my nitrites are .5ppm and my nitrates are (SHOCKINGLY) 160ppm!!!  So I run down to the grocery store and purchase 9 gals of RO water, treat it with Prime (just in case), and do another water change of 25%.  I also added some beneficial bacteria starter to be on the safe side.
I add some aquarium salt (to help bring the nitrate levels down), add a Nitra Zorb packet to one of the filters, wait a few hours and check levels again.  

New readings are 0ppm for ammonia, 0pmm nitrites and 60ppm nitrates (the test card colors are so close between the 40ppm and the 80ppm that it is difficult to tell, but the color looks to be in between them...not quite light enough for 40 but not dark enough for 80) I have an API Freshwater master kit, so i am checking them individually not on a strip test. My ph is 7.4 (but has always been high because of tap water here and I thought Mollies liked higher ph so i was never very concerned with the ph being a bit high)

My Mollies are still freaking but now some of them are flashing!!  I can not see any signs of external parasites, no ick, fungus or anything.  I have a majority of Silver Sailfin Mollies, but I have one Black lyretail and two cremesicle girls, and one of my VERY pregnant cremesicles is flashing!

My baby snowball(1 1/2 in) pleco is behaving fine and his coloring is great, as are my 2 yr old small (2 in) pit bull pleco and a medium Mystery snail.  I can't locate my leopard snail (which has me concerned after finding two snails dead).

When I fed the tank today, I gave them bacterial medication pellets, just in case they had an infection.  I grind it up in a fish specific peppermill for the fry, so everyone got it.  Yesterday they had smashed/skinned defrosted lima beans because I ran out of frozen peas, and it was pea day.  But all my fish had the same thing yesterday and none of the other tanks/pond fish are demonstrating this crazy behavior.

I have a hospital tank set up, but it's only 10 gals and I have at least 15 Mollies behaving weird (some adults some juveniles).  I keep 5 other tanks (ranging from 10 gal betta/dwarf african frog tank to 100 gal Blood Parrot Cichlid/Angelfish/Common Pleco tank, plus a 65 gal pond with shubunkin goldfish and a common pleco outside).  I have NEVER witnessed a this behavior before!

What can I do to help my Mollies??  Two of my beautiful males are displaying this behavior and I would hate to lose any of them because of something I could have prevented.

Answer
Hi Marcie,
It seems like you know quite a bit about fish keeping.  From reading your entry it sounds like you have started a mini cycle by doing a tank transfer.  Or otherwise you would not be getting ammonia and nitrite readings.  A mature tank has 0 readings of both ammonia and nitrite with readings of nitrate.  There are 2 areas that hold the greatest amount of bacteria, the filter media, and the substrate.  My guess is when transfering the gravel over, most of the bacteria must have been left behind during a gravel transfer therefore causing a mini-bloom and a mini-cycle.      

I am glad you are using a liquid test kit.  Many folks use test strips and get false readings because it is very very inaccurate.  160ppm is extremely high and I'm very surprised at how it can reach this high with your two partial weekly water changes.  For fish, I recommend 40ppm or less.  The lower the better.  I keep my nitrate levels below 10ppm because I have delicate invertebrates, but since you have only fish and snails, they can tolerate a lot more.  RO water is perfectly fine but it is expensive, if you want to, you can use plain treated tap water which works just as good.  This new tank must need time to break into cycle.  It shouldnt take long because you have seeded the new tank with used media, along with decorations, plants and gravel.  Your mini cycle will probably last less than a week.  Also, I do want to point out that aquarium salt does not lower nitrate readings.  The only way to get rid of nitrate is by doing water changes.  Think if it like this, whatever comes in the tank must somehow come out and adding more stuff in contradicts it.  In other words, you feed your fish and the food gets broken down into nitrate as the end result, has be taken out of the tank via water changes whereas adding salt, doesnt remove anything but add.  Adding salt only reduces stress and give the fish electrolytes.  

Plecos are usually very very hardy and will be one of the last fishes to die.  Your leopard pleco I bet is perfectly fine.  Another thing I like that you did is feeding them peas.  I also have a pea day scheduled in my week :).  I cant stress that enough to feed peas to fish because peas have been researched on with fish and it dramatically helps their GI system and provide nutrients.  Also it has been known to treat constipation related symptoms.

Agian, I am baffled at how the Nitrate it is so high if you are doing water changes.  Do you have a ton of fish in there by any chance?  You did say it was overstocked, how overstocked is it?  The two water changes might not be enough, or you might not be removing enough water.     
Increase your partial water changes amount every day to reduce nitrates down to 40ppm and try to maintain it there.  High ppms of nitrogen affect and harm fish's gills.
-Matt-