What are the dimensions of your 40 gallon? A 40 gallon "breeder tank is LXWXH 36X18X16 inches. This particular tank can carry up to six Discus. The surface area in this case is enough to violate the general rule of one Discus per ten gallons.
A standard 55 show has only 576 sq. in. and the 40 Breeder has 648 sq in of surface area. Regardless of the volme all Discus tanks should have at least 50 to 75 % water changes twice a week. This enough to make it possible to maintain good water quality in even the smaller tank.
I usually recommend 10 gals/144 sq. in. per fish at a minimum but the 40 described is allowing 180 sq in surface area/fish.
I have successfully raised six discus in a 40 breeder to nice size and ended up with a pair so I have the practical experience to know that this is workable.
If your tank has different dimensions then do use the 10gal/144 sq. in. per fish guidelines.
If it turns out your tank is large enoug to hold four to six discus be sure you do buy the from a Discus specialist. If you try to find cheap Discus you will not get fish worth having. Ouality Discus are never very cheap but compared to reef keeping it is a much more affordable hobby. Your Discus may live more than ten years so why cut corners? Also get all one variety, Avoid collecting sevral types. This is an esthetic issue bt it almost always makes a better looking display if you keep all one variety. If you had room for twelve Discus then a having two groups of six of complimentary colors can also make for a nice display.
I really want to emphasize that you should buy a group of four or more at the same time. Go with a simple set up; bare bottom, a few potted Sword Plants and some bog wood will make the aquarium attractive. It is alright to sprinkle a very thin layer of sand less than 1/4 inch tomake it less stark and it also gives Discus something to poke around for food without becoming a waste trap which is what happens when a normal depth of substrate is used. It can be done but discus keeping and planted tanks are both challenging and separate hobbies. Integrating both is not a bginner's project.
Your lighting is too intense for Discus and I see no reason why they should have to cope with it. Discus are perfectly happy with only a little light. I suggest that you use fluorescent lamps no stronger than is necessary to grow low light plants and to view your Discus.
I happen to keep my Discus at about 84 to 86 F = 28.5 to 30C. I began keeping Discus in 1967 and breeding wild Blues and Browns in 1969 so I have a good deal of experience including commercial Discus breeding. I still breed and sell them but on a less intensive scale and I am going back to my roots and working with wild Discus more although I still raise domestic Discus. Here are a few photos. The first is one of my domestic varieties, the second is a group of wild Symphysodon discus Heckel and the last is another wild, a Manacapuru Blue.