Every so often you will find an aggressive koi, and it looks like you have one. If I were you, I'd try to find it another home in a pond with other koi, perhaps bigger, that will be better able to defend themselves. See if your city has a water gardening or a koi society that might be able to help you rehome this fish. You can google them under: (your city) koi society, or (your city) water gardening society.

The problem in trying to keep carp in the same tank with tropicals is more often the water temps than chemistry, so while the 75-80 may be okay for the little livebearers, it's too warm for Goldies, even Fancies. I'd say 72 - 76 max. If you are sure the fin issues are not from the formosa nipping at them, then logic dictates the only other explanation being that you bought fish that were already suffering from some type of bacterial infection that attacked their fins, so just in case; add Pimafix to the water along with the Melafix. They are perfectly safe used together. I've used both in extreme cases in conjunction with some pretty sophisticated antibiotics and affected cures in what otherwise seemed to be hopeless cases. I'l admit to more failures than successes, but just enough successes to keep me optomistic. In general, Goldies are pretty tough and you can often get them back in shape with just super clean water and light feeding, but once fin rot sets in, it's best to treat it with something designed for the purpose. However, like any other meds, unless dealing with a specific disease that has been correctly diagnosed and the fish aren't yet on their last gasp, the best rule of thumb is to start with something safe and mild, and see how it goes for a few days. If that doesn't work, then move up to something stronger, but as with all meds; the stronger they are, the more easy it is to inadvertantly kill as cure with them. So if your Goldies are suffering from a still treatable stage bacterial affliction, and most common illness in aquarium fishes are bacterial as opposed to viral; with the treatment I described, they will hopefully show improvement within a few days. If not, then go to a broad spectrim antibiotic, such as Amoxicillin. Hopefully, it won't be necessary. BTW: When doing daily water changes in a hospital tank, the last thing you need to worry about is cycling. Good luck.

If you have another air pump, go ahead. Smaller bubbles are better. Tall tanks have less dissolved oxygen, and its important to get as much aeration as you can with goldfish. As far as mixing salt with medication, it depends on what you buy. You are using aquarium salt, right? Not table etc? I know you should never mix quick cure with salt...there are others, but I do not know them. Hopefully some one else knows? You want to buy an anti-parasite medicine designed to fight ich. Not all parasitic meds will fight ich, and avoid anything with copper if you can. But it seems like he could have bacterial too... I say treat ich first, since he definately has that. The red streaks and rot could be bacterial, but could also be severe signs of stress too. Sorry I can't help more :(

Not sure why photos are so big on page and not a link but need to stop doing this and just posting... (ie did years of fish rescue and wish people would read real books on the subject rather then ask "yahoo" (you know what I mean). I will post links in another post too long. Some of my photos when I had to sell my tanks, and rock sculptures (real rocks with "hang on back" type of structure - I have background in arts/arts chemistry and sculpture esp, along with biochemistry, and other sciences.) Here is link to source for those HUGE globes (found on canal street, NYC plastics store, went out of business, looked online for years, then saw a light lamp and realize what they are... ) All had filters, heaters hidden behind plant piles - water in one looks cloudy but was crystal clear - biobugs from environmental source (for huge ponds so on but biologist there sent me a sample)... The globe with Swords (sitting on chinese stand) these need anything with a small hole to sit on them) balance water when filling then stable. (put in place) There was ONE blue betta (only as I was giving them away) after I had four young blue betta sisters - from local breeder - - (heard my oops they often can live together) in that HUGE 75 and as they grew up https://www.flickr.com/photos/21430834@N02/sets/72157624858489949/ https://www.flickr.com/photos/21430834@N02/sets/72157626963975954/ https://www.flickr.com/photos/21430834@N02/sets/72157622020140334/with/3809651178/ ** (they are shipped in horrific conditions, many dead on arrival, with water treated with meds (already stressed) then put in cold bowls most die (I would be at petstore cleaning up their bowls and would be there when they arrive - as well fish are sorted out on tables overseas before being shipped) Pet trade has changed from 60's when most all grown locally in greenhouses - I raised fish and would take them in to stores myself. .............................................................................................. Here is some research from legit sources such as (books) zoology, and studies of fish, as well in their environment. (55 years background, pre vet/oceanography) and more, Health care (meaning I can study rx for fish (trickle down from people rx)...and much betta/fish rescue. Flickr photos of Bettas other (sculpted rock backgrounds) Great book - Bettas, with a special Chapter: Tanks for Bettas by Barron's Each species has very particular requirements, ph, temp, space and I am always stunned at how "advice" is given in online forums with most (not all) having no serious research or knowledge base (many great fish forums) - it's as if the blind are leading the blind and having rescued hundreds of betta's in NYC (about to be dumped down petstores toilet (illegal and cruel) I can attest to the end results. Please go to any libriary or amazon and get some books on the subject - or links below. Seasoned breeders, merchants in the business. As well, breeders keep young adult bettas in single bowls due to sheer volume and knowing most will be sold (Betta talk) but the rooms are heated, water changed many times a day and often with water conditioners in them... temporary housing. In native environments they are found in lakes, rivers, and always in heavily planted environments, even in the rice "paddies" of Japan (where I lived for 6 months) which are HUGE systems, with certain algae, mosses and other water plant forms (snails so on) growing in them, which is a great place for bettas. (until harvest time!) They entered into these systems from nearby rivers... Fish, including Bettas when stressed (not what YOU think is stressful but what is stressful to them)... produce/release stress hormones. Putting two males in a tank - or in the ones with dividers which create huge fighting responses (stress meaning the are constantly releasing adrenal/cortisol interior and the other exterior) (which say to other fish - stay away from me)...and eventually this as the toxins they are, poison them interior, weakening their immune system, and the water as well. As eileenaz states - goldfish (cold water fish) and tropicals (bettas air and water in native environment at leat 82 - although they are adaptable to 78 - air as well)... Goldfish as well need HUGE environments and although many falsely think a smaller enclosure creates smaller fish - in actuality their inner organs are stunted and misshapen causing pain and ill health for them. They are as well "dirty" fish meaning copious waste, and like to "mouth" the gravel (which is part of their manner of eating) stirring up debris. Bettas in the wild do not live in "tiny mudpuddles" (although there is ONE species that during dry spells lives in wet leaves and semi hibernate , some survive when the monsoon rains come, many do not - (many hundreds of types including some who "school"). In the wild the short tail is evident, the longer tail "gene" is bred for commercial purposes otherwise in the wild these fish being attacked and unable to escape another's territory fast would not make it. Guppies (their bodies are often betta size now) with their longer tails (if fancy) are often viewed by Betta's as another betta - as well guppies have slightly different water requirements. I had one female betta that was so agressive even in a 75 gallon, that she would attack cory catfish. The best community fish are those that are in their native environment. I have had huge bowls (see photos, actually lamps up to 50 gallon) with Anubias on wood in the center (small heater, filter hidden behind, spot led from ceiling) with a school of black neon tetras (not true tetras) and they got along fine - wish I had taken a photo. The round shape meant endless "room to roam" and fish could go in and out of planted area. Angela - Tiger Barbs (not a good choice at all - note on this site how many keep a few (2-3) stressed need bigger school and space more then five gallon. Why not just have lots of Anubias (same environment) which needs no soil, tied to wood, (conditions water for betta, make sure proper type) and one betta. http://www.wetwebmedia.com/fwsubwebindex/tigerbbehf.htm http://www.americanaquariumproducts.com/Aquarium_Information.html As you can read here at this great site - many health issues, and not good choice with betta - even if provided places for "them to hide" (why live a life hiding when in proper environment they would be out schooling enjoying themselves, or when stressed nip at betta - All fish need space (read Desmond Morris (zoologist, artist and much more) It was he and his book on aberrant animal behavior at zoos (horrific then and some now still along with road side attractions, bears, tigers in small dirty cramped cages) Just as animals display aberrant behavior so do fish when in the wrong environment NOT seen in the wild. Schooling fish - one or two, three NEVER. These fish school for a reason (instincts) and in the wild these schools measure in the hundreds and thousands, catfish as well. They are ONE individual and should be thought of as one, or else they do suffer from stress. As well just because they are small does not mean they do well in smaller environments - I had 6 - 7 black neons in a 25 gallon. (globe with betta). The old myth one inch of fish for each gallon caused a lot of suffering for decades. I rescued a ten inch pacu once from local PxtLxxd, in NYC - he was in a ten gallon tank... found someone who took him for outdoor heated pond - yeah for him, but I first had to heal his scalded body from fungus as the staff would run a hose directly from the faucets into tanks burning the fish often!!! I have thousands of links - posting a few. (they do not come up in searches now due to placement money google so on). http://www.wetwebmedia.com/ http://www.americanaquariumproducts.com/Aquarium_Information.html