oh no! Fin Rot?!

[Nell]

1~What type of fish is afflicted? Panda Cories and possibly betta.
I lost 1 fish today. It shows signs of frayed fins. The smallest cory in the tank also has frayed fins that appear slightly fuzzy around the edges.
The betta has a very small spot on his tail that looks like it could be the start of fin rot. I will try to include pictures later.

2~What are your tank parameters?
ammonia - 0
nitrites - 0
nitrates- 10
temp - 75 degrees
pH - 7.4

3~ How large is the tank? 10gal
How long has the tank been set up? 3 weeks. fish were added last friday.

4~What type of filtration are you using? Aquaclear 20

5~How many fish are in the tank? What kinds of fish are they and what are their current sizes? 4 panda cories, now 3. 1 betta, 1 apple snail

Tank is newly setup. Live plants and fish were added less than 1 week ago (friday). The tank was cycled with ammonia. 80% of the water was changed after the cycle finished and fish were added a day later. I've been monitoring the water every other day and parameters have remained constant.
The tank contains lava rock and play sand as substrate. Both were boilded before being added to the tank.

I am fairly certain this is fin rot. I have never delt with this before and would like to know how to proceed. What is the best way to treat it?

 

[Apocalypse_Gold]

Normally I would recommend Melafix but bettas don't do well with it. The best thing is very clean water. Try looking for a physical cause-sharp corners on decorations, stupid behavior (like betta wrapping himself around filter uptube), etc. Lava rock can be very sharp-like shards of glass, especially any broken pieces. Where did you get yours from?

 

[An t-iasg]

I agree with Apocalypse_Gold - the lava rock could have sharp edges that can hurt a betta's delicate fins. Bettas love their own little hiding spot. Do you have the plants arranged so that he can get away from the flow of the filter also? Bettas don't like current, but if he has a place to get away from the strong flow, he'll be ok.

I'm not sure about the cories, but 75 degrees is too cool for a betta. They prefer temperatures of 80 or 82 degrees. I set my heater for 80 degrees in my betta tanks. The thermometer reads 80 or 81 degrees. Water that is too cool can be a cause of finrot in a betta. Also, like Apocalypse_Gold said, keep the water clean and don't use Melafix on a betta. If you need to medicate the finrot, I have had success with Jungle Fungus Eliminator (has an anti-fungal and an antibiotic in it) or Maracyn Plus (or Maracyn 1 or 2). Use those meds in a QT tank, and not in the main tank, to avoid harming your new biological filter.

 

[Nell]

I appreciate the replies.

Here is a closeup of the other affected cory. You can see that the fins look feathery or frayed around the edges.

Does this look like a fungal finrot? I took the dead fish to the lfs and the guy reccomended Erythromycin... said it worked well for catfish. Do you think I should give this a try?

As for the betta. I do know that the ideal temp for them is around 80 degrees. I had the temp set on this tank at 75 for the cories, since everything I've read about them suggests that they prefer cooler temps. I intended to raise the temp a couple of degrees when I added the betta, but I guess it slipped my mind. He had been living in my other 10 gallon previously, but I moved him out to make way for some new platy fry.
Thank you for the suggestion about the lava rock. The pieces I have are from the fish store, and they don't seem very rough, but I suppose it is a likely possibility that the rocks could damage his fins. I will look into replacing it with smoother rocks or some driftwood.
The filter does have an adjustable flow rate, and I have kept it low for the betta's sake. He doesn't seem to have a problem finding a peaceful area of the tank to hang out.

My more immediate concern is for the cories though. The littlest one seems to be the worst off, and he's looking pretty poor right now....

 

[FawnN]

That doesn't look like fin rot. It does look like your cory was in a fight or rubbed up against something.

This is fin rot on a betta.

 

[Zagz]

Raise your temp slowly a few degrees, I have cories in a tropical tank and the temp is 78 F. They are thriving and eating like pigs. They sure love algae wafers! If the fin deterioration continues, perhaps you can put the betta in a QT tank and treat the cories with melafix then. I agree it doesn't look like fin rot. You can put nylon pantyhose over the filter intake if you think their fins are getting caught in the intake. The lava rock very may well be too sharp for the betta's fins. Cories are quite active and could also quite easily rub up against the lava rock. I'd follow the suggestions above about looking at the lava rock closely for any sharp edges and if there is remove it from the tank.