Black specks in tank

Question
I've had a 5 gal tank for a few months with just one spotted cory cat in it until 3 days ago when I got a peppered cory cat and 2 mystery snails to go in it. (BTW, I know now that cory cats need bigger tanks and to be in groups, so I'm trying to fishless cycle a bigger tank bc of that).

Anyways, the peppered cory cat died a day ago. He was swimming weird - he couldn't stay on the bottom and would float to the top. If he stopped swimming he would also go vertical and eventually flip over so he was on his back.  One of his side fins was also halfway gone - I'm not sure if I got him that way or not (I should have looked at him closer in the pet store.)

I noticed some black specks in the tank a few days ago but unfortunately I don't remember if that was before or after I put the new creatures in. At the time I just thought they were maybe seeds from the one live plant I have in the tank.  Now there are hundreds in the gravel and there were some on the leaves of my fake plants.

The specks are really tiny (less than a mm), don't move on their own, seem to be a smooth oval shape, are black (maybe brown - hard to tell), and aren't attached to the gravel (I can suck them up with the siphon).

Basically I don't know what they are and haven't had much luck looking online besides thinking maybe they are a type of parasite. Are they from parasites or some other fish disease? Are they related to my cory cat dying? What should I do? I don't want my remaining cory to get sick and die like the new guy did.  The ammonia is 0 ppm, the nitrites are 0 ppm, and the nitrates are about 10 ppm.

Thanks for any help.

Answer
Good evening Allison, thank you for your question.

It sounds like your cory cat was in bad shape since the beginning. I would be especially wary if you purchased him from Walmart or Petsmart. Cories are considered "scavengers" by many, and a less than reputable store will allow them to eat the carcasses of their tankmates, thereby contracting any disease that may have plagued them. Many cory cats are starved in the store because of not being given their own foods. Expected to eat whatever is left of the flake (which is often times little to nothing) they slowly starve. This could be one reason for the buoyancy you observed, a damaged swim bladder could be another. The frayed fins suggest either predation/bullying from a tankmate, poor water quality - or both, certainly.

Now that you know that cory cats may be housed in less than ideal circumstances in the store, I strongly recommend you use your 5 gallon tank for a quarantine tank. There is no need to keep the tank cycled, you can just use 75% of the water from your larger tank to fill it and have the rest be all new, conditioned water. Another alternative is to keep a sponge filter, such as the kind made by Hydro, running in your main tank at all times. When quarantine is necessary, you can move it and use it to cycle or "seed" the QT.

I would vacuum the gravel deeply or, since this a small tank, remove it entirely and rinse it in cool (not cold or hot) dechlorinated water. I would do the same for the plastic decorations. Baking soda can be used as a scrub with no deleterious effects to your water. If you drain the tank, keep your remaining cory and snail in an aerated tub of their old water while you perform the cleaning. It may not be a bad idea to install a loose fitting cover to keep the snail from crawling out, as they tend to do.

I have never heard of black spot disease (BSD) manifesting itself on anything but the fish, but your description matches that of the cysts. I hope this isn't the case, and that a careful cleaning removes the specks. If not, do some reading about this disease using Google. Since "black spot disease" is also a kind of rose blight (the flower) I would use Paravortex and Diplopstomiasis as primary search terms.

Do not medicate before doing a cleaning. If the specks persist and after doing some reading you believe BSD is the case, I would use a medication such as Jungle's Parasite Clear...namely something containing Metronidazole as the active ingredient. Copper is also likely to be effective but would be deadly to your plants and snail. You must remove the snail no matter what medicine you use (if you decide medicating is appropriate) since to my knowledge, no effective medication is "invertebrate safe" in reality.

I hope that helps. Your water parameters are just fine, I appreciate you including these. I don't believe the black specks are related to the new cory's passing. Even if it is black spot disease, this is less virulent than even white spot disease, aka ich. I do believe your new cory had a hard life before you took him in. Do consider using a quarantine protocol to avoid such heartaches! Also, read this brief checklist. It details how to select healthy specimens:
http://freshaquarium.about.com/cs/beginnerinfo/ht/choosefish.htm
Rather common sense stuff, but still worth your time.

Good luck, take care. Feel free to write back anytime!
Nicole