Fin rot bronze corys

[Familyfishny]

Hi folks,

I think that two of my little corys have fin rot. Their dorsal fins seem to be shrinking, and this one in particular seems quite lethargic. I had an underpowered, ineffective filter that I just replaced, and the tank seems much cleaner but this guy continues to decline - or maybe I’m being a fish hypochondriac? I have two questions:
1) does this guy look like he even has fin rot?
2) if so, should I treat the tank to help the two cories who are potentially having fin rot? 1T/20L salt worked wonders for them about six months ago when they were all looking lethargic; should I try that again? Or should I try a medication? Or just wait and see if the improved water quality does the job?

37 gal tank
5 cories, 7 guppies
Ammonia 0
Nitrite 0
Nitrate 20
pH 8.2
gH 180
Temp 72
Penguin filter, bubble wall, sand substrate, 1 sword fern and stone structure/caves

Edited for clarity

 

[Slaphppy7]

Doesn't look like fin rot to me, but hard to tell with the one pic

Never treat for a disease/ailment unless you know exactly what you are treating; fresh, clean water is always the preferred course of action when unsure

 

[Familyfishny]

You’re so right. Is this a better diagnostic picture?

 

[Slaphppy7]

Yes, much better pic....the fin does not look "right", but I'm still not convinced it is actual fin rot

If the fish are acting and eating well, and your water params are good, with weekly WC's, I would just wait & see

 

[Familyfishny]

Thank you! This little guy is lethargic and not showing much interest in food, and his trips up to get air seem labored and slow.

 

[FranciscoB]

What volume of water do you change and how often?

 

[Familyfishny]

50% weekly, more like 2x/week lately due to the crummy filter.

 

[Familyfishny]

The two cories are amazingly still with us, but continue to decline. One now has almost no top fin, and his tail is also rotting away. He is also developing a secondary fungal infection on a pectoral fin. Are these symptoms sufficiently diagnostic to treat with medication? What can I do to save these two and protect the other three cories and the ten guppies?

The water quality is not good. I am doing everything I can think of to improve it, new filter, big water changes, sand vacuuming, adding extra filter media to the new filter. I am hoping to figure it out, but would like to treat or quarantine or something the two very sick cories. Any advice would be most welcome.

Ammonia 0 but spiked to 0.5 last time I sand vacuumed (Tues pm)
Nitrite didn’t test today
Nitrate ~20
Gh180
Ph 8.2
Temp 74
37 gal
Plants down to one ailing sword fern
Aquarium sand and rock with one wood chunk for the BN pleco
Flakes for guppies, 1-2 tiny pinches/day, bug bites 1x/every dayish for cories, algae wafer fragments for BN pleco and cories (cories hog it unless I drop a few) every day or two.

Penguin filter with basic filter cartridge and wheel, ripped out part of cartridge and added a big wad of filter floss and a pre filter on the intake tonight. Ears wide open for wisdom on what to add to improve filtration and stop the filter from overflowing instead of filtering at a high enough volume to turn the bio wheel.

 

[Familyfishny]

What a difference the filter additions made! The filter floss and sponge filter completely cleared up the tank. I added 1tbsp/20l salt, and the two cories have perked up a bit. The fungal fluff on the sicker one’s fin is a little smaller. No improvement in the fin rot, but it doesn’t look worse either. Fingers crossed!