brown algae-how to control with live plants

I'm in the process of migrating from artifial to live plants. My set
up is a 55gal tank, Eheim Professional II Canister filter, Coral Life
compact flourescent light 230 watts. My chemistry is
Ph 7.0
dKH 4
dGH 10
Nitrites 0
Amonia 0
Nitrates 80

For the first two weeks my KH was only 1 or 2. I've always used R/O
water but this I decided to mix some tap with R/O to raise it. The KH
rose to 4 but I think I stressed the fish to much with the water
changes because many of them developed ick. At that point, I began
treatment with meds and bought a heater to raise the temp 85. Shortly
thereafter, i began to notice brown algae on plants.

I have a few questions.

If I stick to R/O water, what can I use to raise it's KH to 3-4?

What is a normal water temp fluctuation? Should I keep the heater on
so the water temp does not drop during the night?

What can I use to eliminate the algae?

BTW, while I'm waiting on the CO2 injection system, I'm using the
jungle fizz from a friend.

Thanks

Jerry

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