There's two general approaches to preventing algae.
1) Starving the algae by keeping the water nutrient poor. Preferably without starving the plants. Which is easier if you have nutrients in the substrate that plants can get to through their roots, but algae can't.
2) Provide plenty of nutrients in the water. This should feed plants and algae alike. But assuming you also have plenty of healthy plants, they tend to suppress the algae; though exactly how isn't known.
You're probably closer to #1 right now. Successfully venturing from that to #2 takes a leap of faith to do it properly. If you try it only tentatively, for example adding a bit of a single nutrient to see what happens, the plants may not be able to utilize it for lack of something else, and it may only feed the algae.
By feeding your fish, you're getting enough nitrate, given your 10ppm NO3. Likely enough phosphate (PO4) as well. But plants also need a source of potassium (K), which fish food is poor in. Plus iron and also other trace nutrients. At bare minimum using off-the-shelf products, I would dose something like Seachem's Flourish and Flourish Potassium to supply these requirements. A lot of folks (myself included) buy dry ferts, and either dose dry, or tailor-make our own liquid ferts. This takes a little learning curve but is cheaper in the long run. I spent $25 on my initial order of dry ferts. Almost ten years and many tanks later, I still have some of the original ferts left.
I'm not sure about your lighting, as I'm not good at estimating light levels using CFLs. But I'd seek confirmation about that if you haven't already. If you were accidentally getting medium light, or very low light, either can cause algae issues. Post details about what kind of fixture your CFLs are in, that will help those who are more familiar with them.
The slimy green algae sounds like BGA, which is actually a photosynthetic bacteria rather than a true algae. If you can post pictures we can verify that ID. Various methods exists for dealing with BGA.
Vals can melt when exposed to Excel for the first time. They typically grow back. But that can be avoided by introducing it slowly. Try adding 0.25mL/10G for the first week, 0.5mL/10G next week, and so on until after a month you're at the normal 1.0mL/10G dose.
Since this post covers a lot of individual topics, I haven't gone into full detail on all of it. Read up a little on anything unfamiliar to you, then post back with any specific questions.
