Question: New axolotl owner, would appreciate some tips!

[Antonis]

Hello! I am a new axolotl owner, and I've had Bagels (my axie) for a bit over a month. I'd like to make sure I'm taking care of him well, as his tank ate unfortunately didn't manage to get pass the many sicknesses he probably picked up in the pet shop. My questions are as follows: Is a 180l tank okay for one axie or is it too small/big? How often should I change the water, and how much of it? I've been doing 30% changes every 4 days. What sort of decor should I get for Bagels that won't be harmful for him? And lastly, although I doubt it's anything, he has some greyish-white spots on his tail which I think may just be his pattern but I'd like to make sure. .
Pictures of the tank and Bagels himself & his tail attached below.
https://imgur.com/a/qAa5Zj0

 

[Hayleyy]

Bagels looks lovely!! First of all 180L is enough for a couple of axolotls, nothing is too big The most important thing for axolotls is floor space rather than height. I follow the rule of 2ft of floorspace for one axolotl, then 1 foot extra for each additional axolotl (minimum).
You can get away with changing about 15-20% of water a week, depending on the nitrate levels.
You can get live plants to give the tank some more colour. There are threads on here with the best plant suggestions (suitable for cold water with little light). Java fern is popular and easy to care for. Plastic/silk plants are fine too (as long as they aren't being eaten- I've never had this as an issue but some people have).
You can use anything aquarium safe, as long as there are no sharp bits. I use ceramic pots and rocks for hides.
The spots on his tale are just his colouration

 

[Antonis]

Thanks for the help!