Nice looking tank and fish.
Other than light, one of the main things plants need is carbon - mainly in the form of CO2, which is very limited in most aquariums and in nature too. Your tank has an air pump running and a HOB, which will be possibly be creating quite a bit of surface aggitation and driving off CO2. Because of this, it's usually advides not to run air pumps in planted tanks, so unless your fish are otherwise showing any signs of oxygen deffficency, I would turn the air pump off
.
One option to increase carbon available to the plants is through the addition of calcium bicarbonate, which is dissolved slowing from tufa rock and crushed coral. Most aquatic plants have adapted to use this at some level because CO2 is limited in thier natural envirnment. However, ths may not be needed depending on your water hardness already, do you know it? Also, this is not a good option if red bellies can't deal with hard water (I've never kept them, so am not sure).
For a couple of the species you have got there (the Amazon swords and
Cryptocoryne sp.), it's recommended to have some sort of source of nutrients in the substrate as they are heavy root feeders. If this is a mature tank of around a year old, and you never gravel vacumed much, then enough mulm may have built up for them.
If not, I would advise some root tabs, which you will need to push in around the roots and replace every few weeks to months depending on the brand.
Tbh though, your gravel looks a bit course to I'm not sure how well those two species will do even with root tabs.
On the left hand side of thw tank you also seem to have a
Cabomba sp., this plant is fairly easy going as long as it gets enough light, and is a fast grower. In lower light tanks, it usually gows long and straggaly, eventually ending up as a floating plant but will grow very fast once it's floating and close to the light.
If you do'nt have any luck with these species due to the gravel, try some Java fern and
Anubias spp. - these plants can be tied down to wood/stone/tank decor and would probably thrive if you tied them onto a couple of your large peices of gravel. They are very easy low-maintenance plants that grow relativly slow (so have low light, carobon and other nutrient demands)and require basically nothing special in the aquarium apart from light for around 12 hours per day, just like any plants
(give or take a few hours).
