[GpsFrontier]

Hello Alec,

What's the best lighting system I could use without needing a ballast?

Natural sunlight. Even a cfl has a ballast.

And my reservoir is 5 gallons

way to small.

so how often should I change the water?

With that small reservoir at least once a week if not more expecting to growing 3 large plants.

I'm using botanicare pro gro hydrogarden vegetative formula for the vegetative phase and their hydrogarden flowering formula for the flowering phase

As I said earlier those plants are continuously flowering/fruiting plants. They don't have a vegetative stage and flowering stage. They do both stages at the same time. That's why their called "continuously flowering/fruiting" plants.

am using the amount it says to use on the side, so I'm not concerned with the nutrient levels,

The manufactures directions are just general guidelines. Plant size, humidity, age, type, temperature, are all major factors to consider in weather to decrease the nutrient amounts. Not to mention the water volume your using.

and has a tendency to form sediment and clog my pump

What color is the sediment? Some nutrients can cause build up, but most don't and and if they do it's likely it's a growers error. Example: If your tap water is pH 8, and you mix your solution in it before adjusting it. You'll likely see white powder like seatmate.

I do regularly check my pH and I only have to adjust it after a water change

By this are you saying that your high pH is due to your tap water? If so you should adjust the pH before adding your nutrients. But you should be using filtered water to begin with.

The water temperature is about room temperature

So what is your high and low room temps? My mom wont turn the AC on if it's below 81 degrees in her house, I like it at 76. I'm not there to check your thermostat. Also sometimes the lights or other factors can result in raising the water temps as well. Especially in such a small reservoir (volume of water).