Flow Rates

[Crazy fishes]

CF here with more questions. Lighting is pretty much understood now; most principles I have read and conquered so to speak. Flow rate is a completely different game all together. If you read threads most aquarists suggest trying to generate to most "turbulent" flow possible. This is because turbulence mixes the water, ideal for gas exchange and nutrient uptake. Most means of generating water flow in an aquarium is by pumps which produce a constant "laminar" flow output. Emmm, a problem how to get turbulence from the laminar. It appears it is all related to the interactions of water with solid surfaces around it. Numerous studies have shown that high flow rates stimulate faster rates of photosynthesis and respiration leading to better growth and overall health of corals. That said these studies are all done with SPS corals like Acropora and Stylophora..... why has no one addressed LPS and soft corals??? Apparently a polyp that half extends its tentacles can be entirely happy where most people would consider this as the coral is trying to say "Get me outta here". Also fast laminar flow gives rise to the most turbulent flow and it depends on which side of the coral the flow is approaching as to which side receives this turbulence. I had this in my tank recently with regards my hammer; flow moves in a circular motion around the tank. The side receiving oncoming current was generally half extended whilst the far side of the coral was fully extended. You would assume that this is because the tentacles are carried by the current but apparently not. It is because the tentacles are extended further into the boundary layer for better uptake of nutrients and photosynthesis, which is easier to do in the slower moving water of the boundary layer.
My interest in flow rates comes from my recent purchases of LPS coral (Euphyllia ancora and Euphyllia Divisa) which responded very differently to the flow that I had in the tank. Previously to this I had GSP and Palythoa; the GSP would not open unless it was directly in front of the hydor koralia nano. Since the LPS have entered the tank, the hydor nano is switched off to see if polyps on the frogspawn will extend fully but no joy as of yet. Since the nano is off the GSP has been emerging and then de-emerging if you get my drift. It is so difficult to get that delicate balance where every coral is sitting in the right flow pattern with the right amount of light. What I would really like is a definitive table or list; Ski was working in his local club on a similar thing with light trying to work out which corals in what PAR do the best. It is annoying when people say that coral likes moderate light and moderate flow. WHAT THE HELL IS MODERATE LIGHTING AND MODERATE FLOW?? How do you know when moderate flow becomes fast/high flow or the converse. I think this is really why marine aquarium establishment and maintainance is so much harder to get into.
If anyone has any suggests on positioning of pumps to achieve the desired flow patterns please reply. Also if anyone wants to help with trying to generate such a list to help new aquarist come over to marine fish keeping please reply also.

Regards

 

[SkiFletch]

Heh, well CF, flowrate is a very difficult concept, ESPECIALLY in smaller tanks, I'll get to why in a minute. The challenge is twofold; To re-create the natural reef; and more importantly, to re-create the specific natural reef where the coral grows (Intertidal, Deep Water, Reef Flat, Reef Shelf). Anyone who'se ever been diving will tell you a few things about the natural reef. The first is that wave action, swell, surge, and currents creates an extremely dynamic environment as far as flowrate is concerned. Especially true on windy, choppy days at the surface, you can be swimming along a reef below, catch a surge, and be tossed around like a ragdoll. The changes are sometimes swift enough to generate uncontrolled ascents/descents (bad), and a real good reason for inexperienced divers to stay away from such bad weather .

These constantly changing conditions really make corals sway and flow. As you mentioned, turbulence abounds. This helps the corals breathe, gain food, ward off predators, and also importantly, ward off detritus, sand, etc. Re-creating that is often difficult or expensive in home aquaria. You really have 2 options: A surge box/wave box like the Tunze wavebox (or some DIY solution), or a frequency modulating wavemaker and multiple powerheads. There are on-off powerhead wavemakers, but these are exceptionally hard on powerheads (mechanically speaking) and lead to their demise much faster than normal wear-and-tear would. Wave boxes are expensive, as are frequency modulators, each costing multiple hundreds of dollars, pounds, euros, whatever. Even here in the states where everyone says things are cheaper, these items are not really affordable to the average aquarist. Furthermore, wave boxes really are impractical on tanks less than 3-4' long as they move a LOT of water. Thus, nano users are left to try and buy or DIY frequency modulators to ramp up and down powerheads on opposite sides of the tank.

Now, next thing to understand is that there are different conditions in which corals commonly grow. The Intertidal zone (10-30' reefs and sand beds near shore) where softies like sinularia, devils hand, kenya tree and others (not mushroom leathers though), elegance corals and even some acropora, are common have exceptionally high flowrates that buffet and crash against the corals constantly. These animals can take a licking and keep on ticking where flow is concerned. Then you have on the opposite end of the spectrum, deeper water reefs (60-150') where flow is often times slower, sometimes laminar, and prone to lots of linear surge and linear currents. One day the prevailing curent may be one direction, and the next another, but there is not too much flow direction change down there. Here we find Euphyllia, bubble corals, deeper water acropora, digitate monitpora, and others. And then somewhere in the middle you've got your reef flat and your reef shelf where conditions change on a dime and the coral never knows what it's gonna get next. Common to this area are Leathers, zoanthids, Acropora, Pocillipora, Stylophora, brain corals, monti caps, encrusting monti, and many others.

Now the difficulty often is re-creating a habitat for say a deep water Euphyllia which likes some moderate laminar flowrate in one direction on tuesday and in the other direction on wednesday, and at the same time having GSP that live on the shallow reef flats and enjoy being constantly buffeted by current from every which way in the same tank... Even bigger of a challenge is mixing all these together in a tank that's only 24gallons in capacity. Sure you can do it in a 6' long tank and have areas of slow flow, high flow, and wavemakers to make everyone happy.

Here I am offering more questions than answers really. Alas there is no "book" on what kind of flowrates corals like/prefer, partly because they are adaptable animals. If you really want to go down this road I suggest 3 things to help you out:

Absorb a lot of the writings of Robert Fenner, Eric Borneman, and Anthony Calfo, as these 3 guys have really done research and seen where these things live in the wild and written volumes about them. They're all also aquarists/conservationists that have decades of experience each in keeping corals in aquaria. Way more knowledge than I've been able to soak up in over 2-3 years of my own research

Second, once you get some idea of coral habitats, try to pick one you like and recreate it. Populating your tank with lots of corals from the reef flat, or perhaps lots of deeper water corals. Sticking to one area makes life easier especially in a 24g

Lastly, use your own eyes and experience to know when your corals are healthy and when they're not. And don't be too quick to move them, often times they are very adaptable animals and can be just fine after a couple days of "sulking"

Hope that helped at least a little.

 

[Crazy fishes]

Hey Ski, once again you come up trumps for me !! What you have said makes perfect sense. I was going down a road that is all too common for me; the science route. Well to be honest I was going in to hydrodynamics territory and the essence of what you wrote has made it clear that is not necessary. I think I will stick with your approach and go by 'natural habitat' now to stock my reef system. I have a 96 litre fresh water tank which has two dwarf puffers and a congo frog in which may be suitable for another reef system in due course. I will maybe be able to move the GSP and Zoa in to that and have the 24g as a Euphyllia and Euphyllia-like species tank.Just something to think about.
It is an absolute wonder isn't it; the natural beauty in the complexity of these systems as well as the stunning visual beauty, of course. Well, many thanks Ski most appreciated. I am now going to visit the structure of reef systems, more on the biology of polyps and look up those guys you mentioned.

Regards

 

[SkiFletch]

Hehe, good luck . I'll see you in a few months after you've looked up everything those guys wrote

 

[chris348]

Blown away by your advice and pointers again Ski.....

Get writing a book and I will buy the first copy.

 

[SkiFletch]

Thanks for the compliments, I ramble too much though