Granted, swim bladder disease was our self diagnosis but seeing that he had a bloated belly and was perpetually floating upside down, it was the most likely disease.  

We moved him to a hospital tank and reached out to some vets to enquire if they treat fish. Here are some vets which we found treat fish:

1. Vets for Pets - Jurong (Dr June Ang)

2. Beecroft Bird & Exotics Veterinary Clinic

Beecroft does house calls too! However, as we started providing swim bladder medication to Gabriel (around 3 days after he fell ill), we monitored the situation. We didn't want to bring him down to a vet since we were unsure how he would take the trip. 

We used swim bladder treatment+ by interpet. We medicated him according to instructions: giving a new dosage on the 4th, 8th and 12th day, doing a water change whenever necessary.

Gabriel also stopped eating when he fell sick. We started to hand feed him ground green peas + water using a syringe around the 4th or 5th day. After about a week of peas, we handfed him ground pellets + water using same said syringe. 

This was adapted from youtube: https://www.youtube.com/watch?v=TAtUVFOlkfU 

No photos were taken of this process as we felt like we were force feeding him and I was really disheartened at this point. (you can refer to the video above though- we did the exact same process)

Gabriel started sinking on 12 Jan and we shifted him to the normal tank. 

He had fungal infection and started lying at the bottom of the tank on 13 Jan. 

The turning point came on 24 Jan where he started swimming occasionally and using the filter to prop himself up. This happened till 26 Jan. 

On 27 Jan, although he was still sinking to the bottom, he no longer laid on the ground. Things continued to improve. Currently, he seems to have made a full recovery and is slowly regaining his colours. He also accepts cuddles these days and we can't express how happy we are!