How do you know if flow is too strong or light too high?

[alexytman]

My corals so far had been high light and flow, but how do you know your coral is getting too much flow/light. I know too much light can turn corals brown because of zooxanthellae. What about flow? Do they close up with too much flow?

 

[TheHarold]

If you are ripping them apart, flow is probably too high.

 

[alexytman]

If you are ripping them apart, flow is probably too high.

What is ripping them apart? Does that mean literally? Wouldn't that mean theyre dead

 

[TheHarold]

What is ripping them apart? Does that mean literally? Wouldn't that mean theyre dead

Flow is so high that it tears flesh off your corals. Thats too high. And yeah, that would be killing them.

In general, for LPS you want a gentle back and forth motion, never pushing it too hard against its own skeleton. For SPS, you can go much harder; pretty much blasting em as long as it is irregular.

 

[KrisReef]

I've had a mag based powerhead fall off of its base and point directly at a coral unnoticed for maybe 12 hours and lost half an SPS colony to the direct blasting flow from a powerhead. Yes, polyps will not be extended during a flow storm, and during that turbulent time your corals are not going to be feeding on any food particulates present in the water column.
(Another clue that your flow is to high is when you swim a fish to death.)

I don't think corals have a set "perfect" flow speed, but there certainly is a range of optimal flow for O2 and nutrient exchange, but that range is probably species oriented.

Many people try to set up their tanks so that the water motion is random and the speed is variable to mimic what happens on reefs that experience tides, currents, storms and the changing water flow that those events produce.

 

[alexytman]

Guys I moved the Duncan and it's in a much lower flow area. However, I realised I ran out of glue. I put it in a hole that is a good fit. Will this damage the coral?. A small part of the base is touching the rock

 

[KrisReef]

Guys I moved the Duncan and it's in a much lower flow area. However, I realised I ran out of glue. I put it in a hole that is a good fit. Will this damage the coral?. A small part of the base is touching the rock

If you are lucky the coral will grow into the rock. This is more likely to happen if the duncan isn't wobbling around in the hole. If it is a snug fit, I would leave it as any "damage" that might occur has already been done when you wedge it into the hole.
My duncans grow like weeds if they are left alone (not moved around), and fed every day. If it looks happy, and it's open I would feed it and hope for the best.