Here is first answer....
I feel this fert is really meant for low light, lower energy tanks where nitrate and phosphorus will be provided by fish food and rotting detritus. In higher light, higher energy tanks this will not be produced fast enough to satisfy the plants.
You need to provide nitrate and phosphate (and probably magnesium) to support your light level.
You will (though may be lucky) not get enough flow using both a 900l/hr & duck bill to support a higher light tank.
You will not get enough CO2 with DIY (I assume yeast). Levels will be far too low and variable and not consistent around the tank, as can be seen from suffering plants.
You need to make the decision if you are going high light and high energy and do it properly or reduce to say only 2 tubes (possible even blocking light from these tubes as well) and go low light low energy low ferts low CO2 and hopefully better plants. At the moment you are neither and plants are clearly showing this.
High tech high energy means...
- Bigger filter, at least 2000l/hr flow rate is recomended.
- Spray bar across while width of tank to get decent flow.
- Supplemented by a power head.
- Proper CO2 source ie pressurised on a timer.
- Decent CO2 injection, ie in line diffuser.
- Very high dosing of fertiliser.
-
ALL TUBES ON
- 50% water changes weekly.
Low tech low energy means
- OK with current filter.
- Spray bar might help.
- OK with DIY CO2.
- Low dosing of fertiliser, maybe twice a week.
-
ONLY 2 TUBES (or less 😵)
- Water changes...whenever.