hi Ahmed. you are already getting great advise from the members here and surely with everyones help your tank will soon be blossoming again.
i think your sump is very poorly designed and indeed quite inefficient. this should be one of the first issues that you should address when you start cycling the tank again.
the first problem i see is that there is a lot of foam build up above your skimmer chamber and the reactor in the second chamber. look at
#1 this is caused by the water which is at the same level in the third and fourth chambers. in each chamber of the sump the water has to be few centimeters lower than in the previous chamber in order to allow the surface of the previous chamber to be skimmed properly. look at
#3. the partition between the skimmer and the reactor chambers could be converted to a bubble trap. look at
#2.
i also think that the filter wool that you have in the fourth chamber of the sump is also quite inefficient because the water is not forced through it but instead it flows over like in
#3 on both pictures.
again if you look at
#4 it looks like the surface of the water is very still. that could be corrected very easily by making the glass
#5 about 5cm. shorter to about the line i marked
#6.
i would seriously consider rebuilding the sump and having it done properly. i love designing sumps and if you like i could send you few drawings, just send me the dimensions of the sump you want and what equipment you like inside. i could even help you with building the sump but unfortunately i live in Swaziland.
oh and
to MASA