What citrus fruit is this?

When we first moved into this house I got quite excited that there was a large lemon tree in the backyard but on closer inspection it appears to be some other type of citrus but I have no idea what...

The fruit is lemon shaped but pale orange in colour (not as dark as an orange). The skin is softish, easy to peel and the segments are easy to pull apart much like a mandarin.
Is it a tangerine tree? Or some kind of mutant mandarin lol

Also the tree is covered in some kind of black stuff...how do I get rid of it in the most environmentally way possible?

Thankyou
from the gardening dunce :p

its not a lemonade tree is it??

Tangello?
The black stuff is likely sooty mould and white oil should help. Buy in garden section of supermarket.
The fruit may be light colored due to malnourishment.
Buy some slow release citrus food while you are at it..
G/L

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its not a lemonade tree is it??

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Wow what's that? It sounds delicious!

ETA: Thanks LTD I'll get onto that. I'm going to try a bit now to see if it really tastes like lemonade!