I would like to know if I would like to know if I would be able to put an Algae ball with some Egerianajas (Narrow-leaved elodea). I currently have them in the same tank. Since, I'm not sure if that will happen, they might be compete for nutrients?
Well, they probably will compete for nutrients, but as long as you have enough in the tank for both of them, it shouldn't matter, in theory. Unfortunately, I'm not familiar with either of the specimens you've mentioned, so I can't predict which nutrients may be the most dear in adding both to the same tank... Hopefully someone else will know. >_o
Egeria najas is in the same genus as regular Anacharis. In fact, E. najas also referred to as narrow leaf anacharis or Asian anacharis. That means that it will most likely be a nutrient hog, like its sister Egeria densa. Algae balls (Cladophora) also appreciate extra nutrients. While they can tolerate low nutrient levels, extra "food" will help it to grow faster.
What is your bioload currently (number and kind of animals, and what size tank)? Are you dosing ferts or planning on dosing?
E. najas however has a higher light requirement than its lower maintenance relative common Anacharis. If you don't have enough light, I'm guessing it will start to shed its leaves. This can lead to polluting your water by both making a mess and causing ammonia spikes. So watch out for that and remove dead parts as often as you can.
Cladophora will tolerate lower light, but high light will again increase its growth. What kind of lighting do you have?
I currently have 1 betta and 1 sailfin pleco in a 5 G aquarium. I'm currently not dosing fertilizer although I have Plant-Gro (Iron enriched) for the Hygrophilapolysperma since it was showing some yellow spots and then turning into holes on the leaves (in another tank). It has an incandescent canopy with Two 7 Watt Sylvania DULUX EL Mini Twist Spiral Compact Fluorescent Lamp (for house use)...