Nitrates do affect fish. Like ammonia and nitrite, nitrate is toxic. It works differently, depending upon the level, the species and the exposure time. It is now understood that nitrates slowly weaken fish, subject to what I just said. So the longer the fish are exposed to nitrates, and the higher they are, the more debilitating to the fish. The immune system will be weakened, stress occurs, and the fish have a harder time just living. And obviously they become more susceptible to diseases they would normally bee able to fight off but cannot now. Ifyou read my article I linked, it goes into more detail.
Second comment is never use test results to determine when a water change is needed. Of course, if ammonia/nitrite/nitrates suddenly increase the emergency water change is often ncessary (depending, just be geeneral for now). But the aim of water changes is stability. Gtting the nitrates as low as possible and keeping them there. It is now recognized that cichlids are affected by nitrates over 20, and nitrate is now believed to be the root cause of hole in the head. Asyou can see, nitrates are more serious than we used to think, or than some still mistakenly think.
First, I already explained that plants use ammonium, not nitrate. They will turn to nitrate if ammonium is not sufficient in balance with the light and other 16 nutrients, but this is sort of a last resort because thee plants take about 24 hours to "switch gears" from ammonium to nitrate, and then they have to convert the nitrate back into ammonium in order to use it. They do not do this unless forced into it, and again the light and nutrients have to be high to make this doable. In your aquarium as in most that are established, there will never be a lack of ammonia/ammonium to cause plants to do this, except in the high-tech planted method (something else).
As for numbers, again I though I made the point...once a few plants like Water Sprite, Water Lettuce or Frogbit get settled--and this is usually just a few days--they will take up ammonia like crazy. And, reproduce. You have 16 square feet of surface, but five or sic Water Sprite within a couple of months will have spread across that surface, and daughter plants appear on alternate leaves at an incredible rate. Floaters are called ammonia sinks, and it continues 24/7. Now, I admit the Silver Dollar may suddenly realize he has gourmet food, that you will have to control. But once these plants get going, one fish is not going to be able to eat them.
On the light. The white LEDs are good, at 6500K. The blues are more likely to get algae issues. There is no red to offset this. If you could use only the white diodes, it would I think be better. I did an experiment with 6500K white and a 11000K blue in T8 a few years ago, and the plants were OK but I did see more black brush algae. When I replaced the 11000K with a 5000K tube, with more red, the algae stopped and the plants did show gains.
looked behind and side of aquariumā¦.I thought he was taken out by the big yo-yos. 
