I have found that lighting that is high intensity can grow micros over Macros IF: nitrates are too high, and phosphates are too high.. and not necessarily together. Reduce the light, use lower wattage, and shorten the time lights are on.. maybe even a half hour will help
In my experience diatoms appear after a new tank set up since 1) nitrates are high, and 2) silicates seem to be higher (probably from poorly washed gravel)..
If your tank has been up for a while, and its diatoms, perhaps you could have your makeup water tested for silicate levels. If this is the problem, a water change might not help much.
All that being said : Introduce some inverts that eat diatoms.. (snails help here):
If you have another tank to hold the cheato for a time, it couldnt hurt to remove it so that some of the foods (sugars and amino acids) leaching from the cheato get rinsed off)
I cant see any harm in a freshwater rinse of cheato.. but doing so will remove any copepods and other critters you may want to send to your display tank
Your caulerpa wont take a rinse.. Mine even die off if my salinity drops because my makeup drip rate is too fast for my small, shallow tank.
Try some of these remedies.. let us know what works best for you.
I really think it helps to spend the money on test kits .. It will give u before and after success, water quality parameters for your tank set up.. and will give u something to shoot for the next time you get a micro outbreak of some kind.
learning this sort of thing is satisfying for me.. makes the hobby a continuing source of interest.. even when I get frustrated as ( bleep!)