I am feeling your pain Cdn_Chica !
Im in a bout of it myself in the 75G and for the record it is not my first time. Let me try the other end of the scale with advice which comes from years of crystal clear waters and also the flip side of having green mucky waters... it is not unhealthy at all to your plants or fish as long as you keep up on water changes and "normal" routines. It will pass with patience OR a UV, Diatom etc... LOL
I have well water and it changes parameters from time to time and season to season. Depending on your well, water temps affect water quality unless treated (Chlorinated City Water). I see it in my water filters on the main line to the house and I see it in the tanks.
Everyone panics at the sight of a green spot on the glass or a change in the water color, it is NATURAL.
It is more a deep slash to our pride then anything else.
GW does not make for pretty pictures, it does not make for good conversation but it is
just a "tank phase" that more folks have been through then wish to admit.
If you dont have the cash for equiptment, in other words, a UV or a Diatom Filter, then just kill your lights, clean the filters good and do water changes every 3 days or so.. it will normally disappear. No need to panic, many of us think that it is harmful and its not ! Its only a slap in the face... LOL
BTW... Please dont tell anyone that I have GW too...
Remember, dont lose the faith, its only a harmless stage.