Righto, option 3 it is then!
Good, not worried then for fin rot passing to my other thread fins. Have done quick searches online, apparently fin rot is most commonly caused by 3 things,
Stress/injury - could be stress from too many males or possibly an aggressive female fin nipped and small damage to tail in which case could cause fin rot to set in
Water parameters - bad water conditions could be a factor, but I do not believe this is the case for this fin rot. As water parameter are really spot on, zero for ammonia and nitrite, and even nitrate is only at 30 ppm at most. 35% water changes done at weekend without fail. Temp at a very steady 25C to 25.5C.
Overfeeding - overfeeding can cause fin rot or other infections!
Right, so believe could be one of the above or more likely a combination of stress and overfeeding being the main culprits of fin rot in this case I reckon.
I've already do not feed fish for one day a week, thinking may increase this to 2 days a week of no food and try not to overfeed on feeding days. (kinda hard to know if overfeeding or not, thats the problem!)
You sure learn a lot in fish keeping, I like learning new things but wish not affected my stock in first place!
When I've test on nano tank later tonight and if readings are at 0 ammonia and 0 nitrite, thats tank is cycled, only took 5 days!!
This will be 2nd confirmation of ammonia and nitrite going to zero within 24 hours just for your info.
Mature media from main tank to Nano tank sure helps a lot!