A Vietnamese eel farmer has revealed the secrets to his DIY water filtration to keep fish healthy.

Tran Khanh Duy said his eels died from tap water when he was starting three years ago in Ving Long province, Vietnam.

The self-taught farmer then researched online for a water circulation system and failed on his first attempt at building.

He tried other approaches until he found the most effective with the use of probiotics.

Footage shows Tran Khanh Duy tending to his pools, which have a centralised water system that prevents fish diseases.

He said: ‘I experimented with it myself and gradually managed to set it up, and now it's working very well.

‘Eel diseases are much less frequent, and the maintenance costs are much lower. It requires less effort and uses only about 20 per cent of the water compared to before.'

Upon setting up the equipment, he first adds probiotics to the system to establish good bacteria.

He said: ‘You then need to add food for these bacteria and monitor the system for about four days. Once the system is stable and the water quality is good, maintenance is minimal.'

Aside from healthy eels, the farmer said there is less waste and he does not need to change the water daily.

He said: ‘Unlike changing water daily which can cause shocks and stress to the eel, this system retains 30 per cent of the water so there are no issues with eel dying.'

For daily care, the farmer said only needs to monitor the system. He said: ‘For daily care, you only need to monitor the system occasionally. However, water changes should be done regularly—every 10 to 20 days for newly stocked eel, and every 3 to 5 days for eel that are six months or older.'

The cost of the filtration system is only 6,000,000 VND (182.98 GBP) while his profit when he sells his 20,000 fish can reach 200 million VND (6,099.33 GBP). This includes two 300-litre tanks, covers, and water and oxygen pumps.

(1 VND=0.000030 GBP)