problem in system

[Sanu Maiya Maharjan]

Hello everyone,

I made growing media bed aquaponic system one month ago using 1 barrel with the capacity of 200 L water for fish tank and 1 for grow bed cutting half. I used hog plum (Choerospondias axillaris) seed as my grow bed as gravel is very expensive. I continuously aerated water in fish tank using aeration pump and air stone. I used Catfish in my tank. 

Now the water in the fish tank become red which make water turbid and also fungus is growing on the grow bed. Also I lost most of my fish.

pH of water: 6.5

temperature: 19 deg centigrade in the morning and 23 deg centigrade at afternoon 

My questions

Can I use UV sterilization in my fish tank to remove red color of water and to illuminate the fungus in grow bed?

Does it harm the fish and plants of my system?

What would be the cause of fish dead?

Does my system required sump tank?

[Cris Meeks]

I would imagine that your problem is your grow media.  The seeds will just decompose & add to the ammonia & nitrite buildup which is probably what is killing your fish.  You're going to have to use a media that supports the proper bacteria colonies to use the fish waste, in other words some form of inert porous stone or clay pellots.  Be careful about fully stocking a tank that hasn't fully cycled, it's usually a waste of money unless you can do regular water changes to keep your fish alive during the process.

[Sanu Maiya Maharjan]

Thank you Cris.
Yes, I already changed water for three times. Definitely I will again review my media.
Thank you for your suggestion.