Update
Thanks for checking on me
In brief:
I treated with Maracyn Plus - stuff came back - Treated with Pimafix - that stuff smells like menthol - stuff came back, but not as bad...
I kinda gave up on Aquaria Central - no one had responded to the last post so I went online and did a bit of research.
Water Conditions (haven’t really changed):
pH 6.8
Ammonia 0
Nitrites 0
Nitrates 20 (dropped to 10 after algae outbreak was cleaned up)
Temp 79 degrees
What I’ve done:
1. Two treatments for fungus and it came back. LFS looked at photos identified it as fungus offered Pimafix as a solution if Maracyn Plus didn’t do it…
2. I treated a stag horn algae outbreak with a Seachem Excel (2x dose daily for a week) and H2O2 spot treatment (30ml applied with syringe applied to plants right before a water change). The water became cloudy with dead algae, nitrates spiked - I started doing water changes 2x a week - 10 gallons each time (33% of a 30 gallon tank). Algae is gone, water is clean nitrates dropped to 10. I've kept up the water change just to see how it goes.
3. Per your advice, I use warm tap water and I don't let the water sit for more than the time it takes to siphon water out - I use 1ml of Prime for each 3.5 gallon bucket - overkill but just in case as DC loves using Chloramine in the water and I'm not taking chances.
4. Started injection of CO2 to replace DIY CO2 – Algae is gone… Anyone want plants, because mine are growing like weeds… I used to love java fern, now it’s becoming a frikkin weed! I have baby java ferns all over the place.
5. Angel is happy, hungry and acting normal.
6. No other fish have died or gotten sick, and are pigs but are becoming a pain as they prefer blood worms to flake food, haha.
7. I am feeding frozen blood worms in the evening, and flakes in the morning. I have reduced the amount just to make sure I don’t make too many nitrates.
8. I added a three baby angels (gift from a breeder friend) and they are all healthy, no "fungus", look beautiful and perky, eating well.
In doing a bit of research online - found the following:
1. Slime coat can increase and slough off from irritation to water contaminants and other irritants. I used to add aquarium salt, 1tbsp per 5 gallons - I read that this stuff can irritate fish and make them produce more slime coat - I'm slowly reducing the amount of salt to the water as I do water changes (So as not to shock the fish). Lets see if that does anything...
2. Unknown disease - fish may die, life goes on... I doubt this as it's doing well and seems happy, loves bloodworms...
3. It could possibly just be sensitive and produce a lot of slime coat - my friend who breeds angels said his fish did the same when he first got them, but they don't anymore...
Since he/she's healthy otherwise I'm at a loss and I've stopped freaking out as the fish, all of them for that matter, seem to be doing well. I would love to know what this is or how to eradicate it, but the Google oracle and fish forums haven't provided any insight
Please see linked videos of the tank and fish. (I apologize about the format, it's the way I held the phone, you can raise the resolution to 1080P and make it full screen):
1.
Close up of the Koi
2.
Tank and all the fish
Let me know if you want me to reshoot the videos