u can get methyl blue too if u have it there for small baths
can u buy small liner like 8x8ft minimum its very small piece of liner must b cheap around 30$ , u can built fairly good size of pond from it 300+ gallon, if u can get more thats better , its easier to maintain larger ponds u wont need to do water changes it will have its own ecosystem , smaller volume causes alot of problem u need to b vigilant and feed less , water changes cleaning etc
Fish Columnaris | Fungus & Saprolegnia | Treatment & Prevention
http://www.americanaquariumproducts.com/Columnaris.html