Bloodworm And Sponge Filtration Options

[Donny041280]

Hi bro's,
Need to ask some questions but i think it's better if i provide my related tank info first, well here it goes..
My data
8 goldies, (7 =3 inch, 1=4 inch)

Tank= 360 liters, 40 watt lamp

Chemistry=
ammo 0
Nitrites 0
Nitrate 25 (after change water 100 %)
Ph 7.2 - 7.6 after buffer 14 tsp of BS after WC 100%
Temp 27-28 c

Filtration
3 ohf with 1650 ltr/h, each has 2 top box filter each, top with 2 blue sponge and 1 black sponge, below with 1500 boyu CR on the outlet i use sponge to drag the current (very minimal current, i'm not lying!!)
Before i add 2 sponge filter with (air pump) the tank has already cycled

Feeding:
Right now im use heavy feeding 4 times FBW 6 cubes each session, and 3 times floating pellets (don't have sinking pellets in here), each session spread through the day in 2/3 hours interval start from 7 am

Water change
Twice a week, wed 60% sunday 100%

Ok, then my question are:
1.my tank is yellowish after 2 days of 100% WC and 1 day after 60% WC is this normal? Or FBW is the yellowish source? (already do water test, and the result is amm, no2,no3=0,0,25)
2.i'm planning to change all my filter with sponge filter only coz this forum recommends it..?! (ease of cleaning, simple, cheap,etc,etc..) And coz in my area the power outage happens everyday for two hours, so if i use 6 sponge filters with AC/DC air pump this eliminate the problem, right? Or no? (right now during power outage i use generator for my home but my OHF consume's 27x3 watt, so to save money on fuel, its better with sponge right? 27x3 vs 5x3 watts)
3.for sponge filters, how to remove the poo? Without siphoning manually? Will the poo desintegrate it self? And where to put it in tank, do i have to spread it evenly in aquarium or 5 pcs in corner then 1pcs in the middle, coz i still want the tank to look good..
4. I currently use guppy brand, is it good?.. Or hydrosponge better,if yes.. where can i find it in singapore LFS?
5.do i still need one ohf for water circulation?
6. do i need to use 6 sponge? Or 4 sufficient..(my bio load is high due to heavy feed)
Thats all, fell free to review and correct my system and do please,please answer my questions..
Thx before !! )