Hi everyone. I would like to introduce myself. My name is Corrado & I am from Australia. I am fairly new to the hobby & have found your site very interesting & informative. However I would be grateful for some help please.

I have a 380 lt/100gal (probably 320lt/85gal of actual water) planted tank. I have about 5 inches of Duplaground substrate with a layer of laterite.
I have about 75 small fish (tetras, platties, SAE, ottos, corys, BN Catfish, rainbows, bumblebee goby & also glass shrimp & freshwater mussels).

I use straight water (I currently do not add anything such as conditioning salts) for the tank through our whole house filtration system using carbon & sediment filters. The GH & KH is approx 2-3 degrees, Ph 7.2-7.4. TDS 100ppm. NH3=0, NO3=0, NO2=0.
I have 8x 39w 900mm T5 HO tubes (I currently only have 4 on 10hrs/day, however they can be switched on in pairs), Eheim Pro II 2028 cannister filter & UV steriliser. No CO2 (my wife insists that I keep it that way!!!).

The photo I have attached is when the tank was 1 month old (only a few fish). Currently things are not too good in regards to plants rotting & leaves becoming transparent. Though no algae apart from some green spot algae. The tanks is now 4 months old.
I was going to start dosing once a week for a non CO2 tank:
3/4 tsp KNO3
1/4 tsp KH2PO4
1 tablespoon Seachem Equilibrium to raise GH.

We are also currently (& permanently!!) on water restrictions & therefore I currently do a 40%-50% WC & gravel clean once a month.

My questions are.

1/ Are my EI measurements OK?
2/ Can I maintain my 50% WC a month or do I need to modify EI doses or WC
3/ How much lighting do I need?

Your guidance on these issues would be greatly appreciated.

Thanks
Corrado