Pulling out the plants would be an option of last resort. But I'll consider it if my tests prove negative.You could try pulling out all your plastic plants, doing a water change and seeing if that clears it up. Sounds to me like one of your (presumably green) plastic plants is photodegrading now that it's been in the tank under lighting for a while and is leaching out material. Bacteria isn't green and algae wouldn't be clear and in any event your UV light would sort that out if that were the problem and the light is working as designed.
No I never removed the plants. The tank is now clear but I am still running carbon. Once the carbon is removed (I'm not intending to use carbon permanantly) I'll wait to see if the green returns. If it does I'll look at the filter sponges then the plants. Why look at the plants last? Well it's going to be quite destructive to the tank to remove them and I'm still not convinced plastic could impart such a colour change. But we will see .Have you tried removing the plastic plants yet? You said it would be last resort but it sounds like you tried everything else.
Yes it was. Fortunately it wasn't harmful to the fish. I'm still not convinced what the problem was (and trawling the internet still none the wiser) but my hunch is that the bio balls that shipped with my media (they were pond bio balls but I doubt they would be much different from tropical) caused a spike in nutrients that caused an unusual strain of bacteria that neither resulted in a bloom or caused algae problems. Possibly fueled by the fact I have almost zero nitrate.What a horrible experience, nice to see an improvement ….