Jebo, Aqua One, Overhead filter type Tanks

If you have one of those type tanks with overhead type filtration, Ceramic
beads with substrate pad above, Dont clean thesubstrate pads in the first
few weeks.
I ran a new tank for 2 weeks set up with plants and all, seeded tank (200
litre) with some fish food at day two.
The cycle seemed to be complete, NH4, and NH3 had subdued, introduced some
fish, 5 tetra + 5 platies + 2 catfish. Everything was fine until, while
checking the filters i noticed that the pads above the ceramic beads were
filthy.
I removed one to clean it, took it away to the trough to wash, and returned
to the tank within 10 minutes.
All the guys in there were looking off.
Tested the water and found the amonium levels were through the roof.
Appears the pads were retaining the deadly chem's, and the water drain from
lifting it out was extrreamly toxic.
I lost 3 within the hour, and a further 4 within 24 hours, and anonther one
withn the 48 hour window due to the lid being closed. The lid being closed
in the first month contribute to the tank being toxic. The riples on the
surface of the water do most of the breathing, and closing the lid causes
the amonia gas tho build up, meaning all the water gets to absorb is amonia
gas. If you have the lid closed for sevel days at the start and open the
lid, you will be overcome by the gases, so imagine what it is doing to the
water.
Rule of thumb, do not close the lid for approx. a month, do not clean the
pad for at least six weeks no matter how filthy they get. Oh and happy
aquariuming.
After the amonium/nitrite/nitrate cycle has completed, you may shut the lid.
Applogies if the order is incorrect, I only know the chem symbols, but you
should get the jist of the cycle from this.