[MUCHO REEF]

When it comes to Palys and Zoas, flow/current and lighting are equally important, almost critical in my opinion. It's simply hard to have a thriving yet successful population of polyps without having them both in adequate amounts. So what's adequate? We had a heated discussion on another sight about the need to measure, (in numbers) the amount of flow in ones tank. It was said that low, med, high and very high flow was not enough to determine the proper velocity and velocity in numbers is what is needed. With this being such and individualized hobby, and we all have our own theories, some right and some wrong, here's my take and it never fails. You can push the envelope on flow only to the point of retracting polyps. Believe it or not, you can even acclimate polyps to a slightly higher flow then they are accustomed to if you do it gradually. Flow in all my systems over the years is simply enough random, oscillating or variable current which wiggles the skirts and the polyp. Yep, it's as simply as that. Mucho, that's dumb? No it isn't, understanding the reason current is so vital is most important.

The best description I can give in understand the vital role in water movement is the one I found on page 404 second paragraph of Delbeek and Sprungs Volume 3 of the Reef Aquarium.

“What’s important about the flow of water is what it achieves. Water motion brings food, facilitates the exchange of oxygen and carbon dioxide with the environment, and enhances the uptake and release of nutrients and waste. It does this by disturbing the boundary layer around a coral head/branch or any other creature”

Water movement also affords the polyps the opportunity to receive a balance of lighting as some may become shaded as they grow down, around and away from the face of the rock they are placed on. Inadequate movement of water in ones system can lead to polyp retraction, yep, it’s true. Over time, detritus can settle and accumulate between polyps. As this buildup continues over time, it can irritate polyps to the point where they are snuffed and less compelled to expand. This is why I use a power head once per month to blast each colony with direct current to clean, clear, remove and rid each colony of such build up. Try it just once and you will see all that flies off your polyps. It is one of the overlooked cause of polyp retraction.

The lack of water movement is also one of the culprits in coral bleaching, most often in hard corals. Adequate/increased water movement also helps heal corals that are already suffering from bleaching.

“Mucho, you’re rambling again”, ok, you’re right. If at all possible, I feel a variable/oscillating current which creates some turbulence is most natural and beneficial. Laminar (Directional flow), won’t hurt, I just feel that turbulent flow from at least 2 different directions is more beneficial and more natural. I achieve this in my system with a Mag 9 return attached to a SQWD. Not much current is generated from this type of return. I used/adjust the return nozzles just to hit places along the top/back of the reef. I have a simple set of Maxi 1200 on medium flow mods kits upping the flow to around 1450. One PH is hidden in the left corner blowing right and bouncing slightly off the left front glass and displacing that flow all over the right side of the reef. I do the same with the right side of the reef. Both power heads also create a nice water ripple along the water surface which help with oxygen exchange and evaporated cooling. I would characterize my flow as medium to medium high. Everything moves, wiggles and sways with a natural motion. Everything is Delbeek and Sprungs description in paragraph 3 above is achieved easily and inexpensively. Sure there are more efficient ways to get more bang and performance with controllers, wavemakers etc, and those are great avenues to achieve a thriving reef. I simply chose a cheaper means as zoas and plays not have the necessary high flow requirements as seen with SPS corals.

Sorry for the long rant.

Mucho

PS, it is very easy to determine excessive/too much flow. If the skirts are being blown over the oral opening, this is too much flow. If you are able to gently wiggle the skirts to the point that they won't retract, then you have found the optimal flow for your polyps. It's just that simple. Again, this does not hold true for SPS.