For this aquarium size, that 500g cylinder won’t last long even if you’re just aiming for 10-15ppm CO2
JBL offers an
adaptor to change over to a refillable cylinder (which you’ll likely still need to purchase the JBL cyclinder - email JBL for fitting details) BUT confirm that local gas company can do the refill (you may need to purchase a special adaptor for the shop to use)
If possible I’d return this JBL kit and purchase a CO2 system from CO2Art (that may be used with locally available CO2 cyclinders or Fire Extinguisher etc)
Do you have the reflectors for your Juwel T8 System?
T8 tubes are significantly lower intensity than same length HOT5 ( VHOT5’s are also available, depending) - note most T8 systems are not compatible with HOT5
Select suitable plants with lower light requirements, especially those planted at the substrate level (60cm water column depth is a challenge ...
there are some lighting suggestions in this previous topic)
Note shading from hardscape etc
Without additional lighting, consider an island style scape that is centred under the light fall