I always thought zoas and palys stretching is caused by lighting issue. Added T5s on my Hydras and they are still the same. Added more flows and they eventually went back to normal.
Yes, it's a combination of both to most species. Flow will help a lot in many different issues keeping all zoanthids healthy in our tanks. Gotta find the sweet flow though. Some areas in nature has very low flow and they are still very close to the rocks due to the strong intensity of light. Those polyps have the most amazing colors!!!
Some species of zoanthids will have long stalks in nature or under high intensity metal halides. That is the way those species are, naturally.
You can keep zoas under LEDs only and have them growing very close to the rocks with a "good flow" rate too. I was able to do that with many species when I tested LEDs.
The fact that they don't look like they are starving for light because they don't have long stalks while under LEDs still doesn't mean the light they're receiving is optimal (see post # 2). Starving for light isn't directly related to long stalks. Yes, I know that normally the term is used for low light intensity situations.
Zoanthids and corals can starve for light because of a lack of QUALITY, very different to what they used to get in the ocean. But they are highly adaptive to our tanks and will still survive. That's why it's all so relative. People don't know if they are surviving or if they are thriving anymore.
Metal halides with T5 supplementation is the best to resemble the natural environment they come from IMHO!
Most zoanthids in the hobby come originally from extremely shallow waters where a combination of high water flow and high light intensity is the rule!
To illustrate everything that I've wrote:
It is kinda rare to find them in deeper waters:
There are many "gurus" in the hobby spreading the myths... they act like doctors making their YouTube videos and just because they sell zoas and corals doesn't mean they really know what they're doing to keep them in optimal conditions. What they do works because of the high adaptive capability of those polyps they keep. That's it!
But this is only my personal opinion and the way I see because everything became so relative nowadays.
I just wanted to make sure and register my opinion in regards to light to keep zoanthids in general.
I know that everyone will see it differently.
Enjoy the videos.