Backyard Aquaponics
A place to discuss aquaponics

Thought that might be the case Omek... your pond was probably more like 25 degrees...

You need to shade your tank and trun your water over as much as possible...

As this is a new system... it probably isn't cycled as yet... that is... the bacteria wont be converting ammonia into nitrates...

5 adult fish in 1000L shouldn't be a problem... but with only a small amount of filtration and uneaten feed... at those temperatures.... the feed will decompose rapidly... and become ammonia...

You might be running the risk of turning your tank into a "fish broth/soup"...

At 30 degrees... water can only hold half the oxygen that it can at 25 degrees... so you may also be low on oxygen....
(you might be able to pick up an air pump and two/four...airstones from the ebay seller I linked to)

In your case... I would immediately stop feeding, remove all uneaten feed... do a 50% water change... get a test kit and test and post results here... shade your tank

Also your growbed looks like it might have "limestone or marble" rocks... these will keep your pH around 8.0 or worse... you might have to replace them...

I would also increase the depth of the rocks to as high as you can within the growbed... around 30cm would be best...

If your pH is around 8.0... and your water temp 30 degrees... your ammonia tolerance is very low.. and could be fatal... here's a chart for you...

why should i use a pure sea salt? why not the salt from the shop?

Normal table or cooking salt may be "iodised" and/or have anti-caking agents in it... either may kill your fish...

Most "pool" salts used in swimming pools... are seasalt... but it would pay to check first...

i've give my fishes a shed just now.. and the result is they finished up all the pellets faster than usual..

Glad to hear it Omek

and now im thinking of how the wastes are sucked up into the grow bed.

i didnt understand how can the nitrites exist in the grow bed. is the nitrification process done in the fish tank or in the grow bed?

The vast proportion of the nitrification is done in the growbeds Omek... the surface area contined on/around the media greatly exceeds any area elsewhere in the system...

Yep, your grow beds are your filters that just happen to grow plants as well. Or at least that is the idea.

is it the uneaten pellets that cause the water to turn cloudy after pellet feeding?

Yep.... and a sign that you're over-feeding...