First time gill stalk fungus & potential columnaris

[Splashme]

First time axolotl keeper, had a wild type about 4 months now in a 200L tank, and guess my little buddy is about 7 months old.
Noticed a patch of fungus on 1 gill stalk, tubbed & tea bathed for 20 minutes in organic English breakfast twice (once per day), and the fungus fell off within 48h and has completely gone (yay).
I'm keeping the lil fella tubbed for 2 weeks, has 8 days left now, seems to be happy and is still eating, pooping, and interacting which I'm happy with.
Changing tub water after about 18H (18L dechlorinated with prime 15/25 RO/TAP mix in tub and temperature matching).

I did though also notice a small patch of white (not fluffy) near on his mouth, it's hard to get a picture, not sure if coloring or if potentially columnaris?.
I've some zebra danios in the tank also, couple died as there mouths seemed to get stuck open, also noticed a few missing so expect he ate them.
Expect this to have been columnaris due to new tank syndrome to some extent, or perhaps bad fish.
Tank was cycled, but nitrate/GH/KH was a bit high at 40ppm until I got an RO filter, maybe had an ammonia/nitrite spike too but I didn't ever manage to capture/measure one.

5 danios now left in the tank, all seem Ok, replaced 50% of the water last week, will do another 50% today, and another 50% next week, then hope to put Axolotl back in.
Also taken all wood, plants, out, changed airstone, replaced polypads, carbon, added extra media & threw away a cheap sponge filter.
Also planning on putting in a better-quality electric internal sponge filter and filling with nitrate pads and filter media as even with 15/25 RO/TAP i'm getting 5-10ppm nitrate.

Questions finally.

• Should I put aquarium salt in the tank, perhaps a couple of tsp, ready for lotls return?
• Would Fritz A+ Aquarium Salt be Axolotl safe if I were to put aqua salt in?
• Does plan sound effective enough to heal potential columnaris?
• Should I quarantine and treat the fish too before housing back together? (I know there's risk with danios & lotl but I risked it, and won't get more more. Tempted to rehome but he likes to eat them.)
• Am I missing anything?

Params now Ok & stable with 15/25 RO/TAP (hard water area)
PH 8
GH 6
KH 9
Nitrate 10
Ammonia 0
Nitrite 0

Thanks for reading and apologies for the level of detail/context.

 

[JM29]

Hello,
Your axolotl will end up eating all the danios if kept together.
Since you suspect your danios to carry columnaris (which is a contagious bacteria), you'd better separate them from your axolotl.

 

[wolfen]

your ph and kh are high but tolerable (expected with hard water, high calcium carbonate), your gh is on the low side but manageable (can be increased with magnesium sulphate)
link to ideal/tolerable levels Water Quality Explained: How It Can Affect Your Axolotl's Health - WSAVA 2015 Congress - VIN
using 50% holtfreters with help prevent fungus and keep your axolotl healthy.
because you have hard water calcium chloride and bicarbonate of soda aren't require.
link for holtfreters here Axolotls - Requirements & Water Conditions in Captivity
also add 0.1g per litre magnesium sulphate (epsom salts)
zebra danios although community fish are known nippers.

 

[Autistic Catholic]

Yes. You should quarantine any fish you are feeding to your axolotl. As it seems you are planning on keeping the Danios in the tank as some sort of feeder fish since you say your axolotl likes to eat them, they should be properly quarantined before feeding to make sure that he cannot receive any disease through the eating of the fish.