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Fin rot - dangling piece of fin - snip it off?!

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Hey folks! Long time no post. I've got a bit of a situation here that I'd love to get some advice on.

I have a wee fish named Sugar who appears to have fin rot, and on top of treating the rot itself I'm faced with the issue that the rot has progressed from the inside of the fin leaving the two outer "struts" of her fin intact but increasingly thin. This morning I discovered the bottom "strut" has now snapped and the bit that's snapped is dangling and swinging around while she swims. My instinct is that it needs to be snipped off, but I want to get advice - whether to do it, and if i should do it, how I should do it.

EDIT: i was writing this post last night and hadn’t finished because i need to take more pH & kH tests and get my head round whats happening with that (and see if im really just awful at doing nitrate tests) BUT this morning her dangling bit of fin looks noticeably frayed and theres bits on it idk if they are loose skin or stuff growing but either way it looks dead as heck and really?!?? Looks like it needs to come off?!?~? So i’m posting this now as-is to see what ppl think. the photos are from last night and dont show the "fraying"


With the fin rot: when I initially noticed the fin loss I stepped up the water changes, treated the whole tank with 0.1% salt and the fin loss appeared to halt. I thought it was okay and just a matter of time till regrowth, and it stayed the same for several weeks, but today noticed that it had deteriorated again and the snappage had happened. I've now removed her to a hospital tank and treated with 0.1% salt again.

  • Test Results for the Following:
    • * Ammonia Level(Tank) home tank: 0 hospital 0
    • * Nitrite Level(Tank) home tank: 0 hospital 0
    • * Nitrate level(Tank) need to re-test tomorrow - looked up the instructions again and may have been doin it wronnnggggg
    • * Ammonia Level(Tap) 0
    • * Nitrite Level(Tap) 0
    • * Nitrate level(Tap) need to retest tomorrow
    • * Ph Level, Tank (If possible, KH, GH and chloramines) 7.2 home tank 7.4 hospital tank
    • * Ph Level, Tap (If possible, KH, GH and chloramines) 8.4 THIS IS NEW holy cow. i dont remember it being this high before. we are on rain water but there are several things i'm thinking of that could be a culprit, new water tank for example ... i dont really know but there have been changes to things
    • Other Required Info:
      • * Brand of test-kit used and whether strips or drops? API liquid
      • * Water temperature? 22 degrees C
      • * Tank size (how many gals.) and how long has it been running? Two hundred litres. A year and a few months.
      • * What is the name and "size of the filter"(s)? Two filters, 200L and 100L, Aqua One
      • * How often do you change the water and how much? I change weekly, my standard water change is approx 1/3 of the tank but every second or third week I change ~50%
  • * How many days ago was the last water change and how much did you change? One day, ~40%
  • * How many fish in the tank and their size? Five fish including the one I have now removed: two are 9 grams, one is 15 grams, one 14 grams, and my big girl is 31 grams.
  • * What kind of water additives or conditioners? We are on rain water so I don't usually use water conditioner. I have been using baking soda to buffer the water.
  • * What do you feed your fish and how often? Give the brand, type of food (sinking/floating pellets, gel food, steamed vegetable, etc.), and how frequently you feed each. Hikari, once a day (i have been feeding a little more than ideal in one sitting because Sugar is completely blind and terrible at finding the pellets, so I've been reluctant to feed twice a day). Every few days I give them all peas.
  • * Any new fish added to the tank? No
  • * Any medications added to the tank? Dosed entire tank with salt when I first detected the fin rot @ 1 gram/litre of water
  • * List entire medication/treatment history for fish and tank. Please include salt, Prazi, PP, etc and the approximate time and duration of treatment. As above, I've now moved her to a hospital tank and treated her with salt again.
  • * Any unusual findings on the fish such as "grains of salt," bloody streaks, frayed fins or fungus? Loss of left side of fin; this has happened from the inside so that a thin outter margin of the original fin has remained. Pics above.
  • * Any unusual behavior like staying at the bottom, not eating, etc.? She was more shy and less active than usual, but now I've taken her out of the main tank she is back to normal.

I live in new zealand and cannot purchase over the counter antibiotics. I'm looking into whether I can get them from ebay.

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Please read our guidelines for healthy goldfish.  I think you already realize that you need a larger tank for five goldfish, but you will also see that you need more filtration and more water changes.  Fin rot nearly always results from poor water quality.


You taught me something.  I had never heard of alkaline rain before, but a quick search told me it happens.  Add some baking soda to the rainwater and see what happens to the pH.  Rainwater has virtually no KH, so the pH should settle down and come out much like the tank water.  That means changing a lot more water should not bother your fish.


Do you see damaged tissue along the edge of her fins?  Could the fin damage have resulted from an injury rather than disease?  To me, the fin edges look normal on the rest of the tail, but you can see better than I can.

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Upping the water change size is no problem, and i'll look at the filtration (a second 200litre filter has been on my wishlist for a while) as well as tank options. I have been monitoring the water quality, but not as often as i should have, so I will get back on top of that - I have been thinking that the water quality was good with the changes I've been doing, but I may just have not been testing enough. I probably did under-sell myself wrt how much water i change, because i do tend to hoover a lot when I change so i end up emptying, refilling, and then seeing more poo and draining more water out getting it,  looking on the calender i can see more 50-80% changes than i remembered doing when i was writing this. Whiiiiiiiiiich just sounds defensive now i'm writing it after your comment. But. Anyway.


It's possible it could have come from injury. I did actually think that when I first saw it, because it was like one day her tail was normal and then the next I was like "wait, what happened to the other half?" - but I wasn't sure that I hadn't just failed to notice it before just with her colouration and the other half of her fin kind of hiding it as she swims, and there wasn't any ragged edge or anything. My filter intakes are covered and my tank decor is all silk plants and smooth rocks so I'm a bit mystified about how she's done it if it is an injury but I guess you can never underestimate them (and the blindness probably doesn't help). The rest of her tail looks completely normal and so do her other fins.


Can you tell me anything about this dangling bit? Am I right to want to remove it? Would boiling a pair of sharp scissors and using them to snip it be appropriate? It is very thin.

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Snip it off at the break.  It won't heal.   Scissors should work or pet nail clippers.  An alcohol dip should be adequate disinfection.

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