[Vicious]

Is this a racing bird? This type of excess urine can be caused in the morning prior to feeding, of if a bird is nervous and disturbed by something, that sounds like it as you say pigeon is more active than normal. But at the same time "rice water" poops can be a sign of a inflammation in the bowel caused by a pathogen. So it is best to take the poop to be checked at the vet. Unhygienic conditions will not cause this poop as if bird is stress by filth, but unhygienic conditions will cause disease so always try to keep the place clean. If that is cardboard and it is not swapped for fresh sheets regularly it can easily mold, or even help bacteria develop on it.

I agree with SilverFeral, what I see is bowel inflammation which could be caused by a pathogen or food.

 

[Vicious]

I I always leave a deep bowl of budgie seeds mixed with pigeon seeds (small seeds are easier for him to pick up). I've seen him pick some up but drop it - he's still learning co-ordination and how to swallow. I'm a bit stuck at the moment because he isn't eating seeds, so I'm having to hand feed him formula 2x a day. The formula I'm feeding him is for hatchlings (0-20 days), so it's definitely not the right stuff. But I'm not sure what to do. I think I might force feed him half the formula + seeds and then just formula at night, hoping that he'll recognise the seeds as food. Should I do this today given that his weight is stable? He's currently 420 grams.

Let it practice eating. I wouldn’t force seed down his throat. Continue with formula in the morning and let him try the seed on his own. In the meantime try to find some frozen peas and thaw them out 30 peas, 3 times a day, unless you replace one meal with formula. Then it would be . Formula. 30 thawed green peas. 30 thawed green peas. Try to get as many of the 30 down as you can but monitor the crop to make sure it isn’t getting impacted.