It seems that circulation discussions always focus on flow (x number of gallons per minute). What about velocity (feet per second)? How much velocity is too much? If you could flow 1000gph through a 1" return, or 1000gph through a 1/2" return, in say a 6' tank, which would you choose, and why?
Flow vs Velocity
- Thread starter madrefkepr
- Start date
I find that total turn over for me works. I have a 4 foot tank. with two tunze 2002 turbelles. 633gph for each. so 1266gph. I have one maxijet 1200 ( 295gph) and a 700gph sump return..
I have the tunzes' turned down to about 500gph each. so about 2000gph total... I have the main return on a 3/4"line then reduced to a 1/2inch lockline nozzle... everything is good.
i am getting some cyano on the sand. I dont have enough velocity down towards the top of th sand. but when i direct the flow down there i disturb my DSB. so i am at a loss both ways....
my corals love the flow. no problems on the rock and such. just the sand....
maybe i am just rambling
I have the tunzes' turned down to about 500gph each. so about 2000gph total... I have the main return on a 3/4"line then reduced to a 1/2inch lockline nozzle... everything is good.
i am getting some cyano on the sand. I dont have enough velocity down towards the top of th sand. but when i direct the flow down there i disturb my DSB. so i am at a loss both ways....
my corals love the flow. no problems on the rock and such. just the sand....
maybe i am just rambling
LA,
You bring up another point that I have often wondered about, that kind of goes along with my original question. That would be concerning multi-directional flow.
Seems to me that ocean currents run in a single direction, most of the time. I'm not talking about currents created at the shore, or in a lagoon, or hitting rock formations, but the overall ocean currents. Only objects in the path of the current change it's direction. So a coral at the "peak" of a reef hypothetically get water movement from the same direction most of the time and do just fine. So why is it that we so often use elaborate, multi return systems, or rotating return devices and such?
You bring up another point that I have often wondered about, that kind of goes along with my original question. That would be concerning multi-directional flow.
Seems to me that ocean currents run in a single direction, most of the time. I'm not talking about currents created at the shore, or in a lagoon, or hitting rock formations, but the overall ocean currents. Only objects in the path of the current change it's direction. So a coral at the "peak" of a reef hypothetically get water movement from the same direction most of the time and do just fine. So why is it that we so often use elaborate, multi return systems, or rotating return devices and such?
Pumps and powerheads are said to produce a uniform laminar flow. Provided they are not connected to a device that will change that ie ocean current or power sweep devices. Corals on the reef are subject to wave action that does in fact alter the flow across the reef crest. However this flow is often tidal and changing on a daily basis. Some areas have multiple tides in a day. Seasonal changes occur as well which can alter the angle in which the same waves reach the reef crest.
Using multiple outputs in our captive systems attempt to achieve nearly random turbulent flow. This can be done using two powerheads pumping towards each other. There will be an area where the two flows converge thus giving a better mixture of watermovement. Some advocate the use of the wavemaker units as well. If given the choice of pure laminar flow or turbulent flow I'd go for more turbulent flow. At least as much as my particular corals can handle. That's just me however and this is an area up for discussion. Some may disagree.
mzem
Using multiple outputs in our captive systems attempt to achieve nearly random turbulent flow. This can be done using two powerheads pumping towards each other. There will be an area where the two flows converge thus giving a better mixture of watermovement. Some advocate the use of the wavemaker units as well. If given the choice of pure laminar flow or turbulent flow I'd go for more turbulent flow. At least as much as my particular corals can handle. That's just me however and this is an area up for discussion. Some may disagree.
mzem
hi.madrefkepr":2w8e9wz2 said:
The velocity thru the 1/2 inch will be four time faster than the 1 inch. This is not important, except:
1, it will take more energy to do the first case (higher wattage pump).
2, back pressure will be higher, and some pump can not handle it well.
3, some livestock may not do well near the outlet... think of it as powerwashing.
I don't want to answer this. You decide.
I would choose the larger opening. I think you want to move as much water as possible while keeping velocities low. If you go out on the reef your entire body will be pushed easily along by the current or surge, but usually at a slower velocity than that found coming out of a power head.
I have subscribed to what mzem suggests. I have 2 returns at each end of my 6' tank. By pointing the flows at each other, turbulence is acheived. The amount of turbulence (flow) is regulated by gate valves. I also can focus or pinpoint the return flows by restricting them via 1/2" bent tubing (upward/downward flow) that I manually stuff into the 3/4 returns. This mostly allows me to direct turbulence to other areas of the tank other than the middle. Sort of a poor man's Tunze system
Any rate, I vary the flow rate/turbulence etc. manually a couple times per day. Sounds like a headache but it only takes a couple minutes to completely change the flow, approximating chaotic flow regimes on shallow reefs. The above setup allows for almost unlimited flow options, yes I do laminar flow as well from time to time.
A low tech (cheap and successful) solution in a high tech world. Works great for me. Next... Bourneman's surge device to add to the mix. 8O I bought the parts. Here goes...
Any rate, I vary the flow rate/turbulence etc. manually a couple times per day. Sounds like a headache but it only takes a couple minutes to completely change the flow, approximating chaotic flow regimes on shallow reefs. The above setup allows for almost unlimited flow options, yes I do laminar flow as well from time to time.
A low tech (cheap and successful) solution in a high tech world. Works great for me. Next... Bourneman's surge device to add to the mix. 8O I bought the parts. Here goes...
mzem -
I understand what you have described, but this would be assuming the reef is fairly close to shore, and in fairly shallow water. This would be the case most of the time, I believe, when talking about the corals housed in our tanks. Now I don't know all the geographical locations of most of the reefs, so I may be way off base here, but what about reefs say 20 miles offshore, in maybe 50 feet of water? Except in maybe severe weather, wouldn't the currents in such a location remain pretty constant? I thought currents were similar to the jet stream, in that the path may change, but the direction stays the same?
Dan -
That is pretty much what I was getting at, the speed at which water moves across the reef. Not having had the opportunity to do any diving the couple of times I have been to the ocean, I'm really only guessing. I have seen closed loops running around 1300gph, through six 3/4 inch returns, and that just doesn't seem the best way to create water movement to me.
Robin -
C'mon, I really wanted you to decide! :wink: These were all numbers I pulled out of nowhere. I guess I am having a hard time understanding why velocity would not be important. doesn't the speed at which water moves over a coral have an affect on it?
Mogo -
Yes, cheap is good! I also change the direction of my powerheads on occasion, but more like weekly.
I understand what you have described, but this would be assuming the reef is fairly close to shore, and in fairly shallow water. This would be the case most of the time, I believe, when talking about the corals housed in our tanks. Now I don't know all the geographical locations of most of the reefs, so I may be way off base here, but what about reefs say 20 miles offshore, in maybe 50 feet of water? Except in maybe severe weather, wouldn't the currents in such a location remain pretty constant? I thought currents were similar to the jet stream, in that the path may change, but the direction stays the same?
Dan -
That is pretty much what I was getting at, the speed at which water moves across the reef. Not having had the opportunity to do any diving the couple of times I have been to the ocean, I'm really only guessing. I have seen closed loops running around 1300gph, through six 3/4 inch returns, and that just doesn't seem the best way to create water movement to me.
Robin -
C'mon, I really wanted you to decide! :wink: These were all numbers I pulled out of nowhere. I guess I am having a hard time understanding why velocity would not be important. doesn't the speed at which water moves over a coral have an affect on it?
Mogo -
Yes, cheap is good! I also change the direction of my powerheads on occasion, but more like weekly.
hi.
Water velocity and other physical property (direction, "chaosity," etc.) does not affect coral other than the following:
1, nutrient transport and waste removal
2, growth morphology
3, tissue damage from erosion and impact of object transported by water
I am going to restrain myself from giving explicit decision so that I won't be called a reef-Nazi. :lol:
Water velocity and other physical property (direction, "chaosity," etc.) does not affect coral other than the following:
1, nutrient transport and waste removal
2, growth morphology
3, tissue damage from erosion and impact of object transported by water
I am going to restrain myself from giving explicit decision so that I won't be called a reef-Nazi. :lol:
Dave
You make a good point, however depth will have more to do with it than distance offshore. A reef crest 20 miles offshore but still only 6-10 feet deep would be much the same in regards to a similar reef 2 miles from shore.
What I had to say earlier about variation still holds true even at depth. Granted some areas may have a smaller net change from seasons or tides. Other areas can totally reverse direction seasonally or with the tides.
I'll use the Flower Garden Banks as an example. These banks lie about 105 miles off the coast of Galveston, Tx. They are also in water depths of around 60 feet to about 360 feet. At least according my nautical charts. This area of the Gulf of Mexico is also notorious for loop currents and eddys that spin off from the general flow of water around the gulf region. Sometimes upwards of 2 knots. While these are mostly surface currents the same currents affect overall flow at depth as the current spirals downward in deflection. Again being random events that changes as the seasons do.
Without getting too much into physical oceanography that is the best I can do. HTH.
mzem
You make a good point, however depth will have more to do with it than distance offshore. A reef crest 20 miles offshore but still only 6-10 feet deep would be much the same in regards to a similar reef 2 miles from shore.
What I had to say earlier about variation still holds true even at depth. Granted some areas may have a smaller net change from seasons or tides. Other areas can totally reverse direction seasonally or with the tides.
I'll use the Flower Garden Banks as an example. These banks lie about 105 miles off the coast of Galveston, Tx. They are also in water depths of around 60 feet to about 360 feet. At least according my nautical charts. This area of the Gulf of Mexico is also notorious for loop currents and eddys that spin off from the general flow of water around the gulf region. Sometimes upwards of 2 knots. While these are mostly surface currents the same currents affect overall flow at depth as the current spirals downward in deflection. Again being random events that changes as the seasons do.
Without getting too much into physical oceanography that is the best I can do. HTH.
mzem
This is one of my favorite topics. In my opinion you want to maximize your flow and minimize your velocity. Huge flow at low velocities is the way to go. The problem is that this is very difficult to do. (to get a velocity of just 1 ft per second flowing through my 28"X28" 10' long tank would mean a total flow of 2,400 gallons per minute!!! (if I did my calculations right!) Of course this doesn't take into account all the rocks it has to flow around or the 6" of sand in the bottom but the 200 gallons per minute of flow I have still isn't getting anywhere NEAR natural levels.
There are also a TON of variables. Things like entrained flow which are practically impossible to really calculate.
I personally try to keep all of my flow rates under 4 feet per second. This seems to be a point where it doesn't create to many problems from tissue damage, etc. unless the water is right up against the output. (at least for most SPS).
The best methods that I have seen to actually measure true water flow is to place small squares of disolvable materials througout the tank for a specified time and then measure how much of each one disolved. Flow in most reefs runs about 2 ft per second but this is 2 ft per second over the entire reef, not just the part in front of a pipe outlet.
I think the propeller pumps are a big start in the right direction with a large cone shaped output that creates a lot of flow with limited velocities.
I'll try to find some of my old links on the subject.
FWIW, Nathan
Of course this doesn't take into account all the rocks it has to flow around or the 6" of sand in the bottom but the 200 gallons per minute of flow I have still isn't getting anywhere NEAR natural levels.There are also a TON of variables. Things like entrained flow which are practically impossible to really calculate.
I personally try to keep all of my flow rates under 4 feet per second. This seems to be a point where it doesn't create to many problems from tissue damage, etc. unless the water is right up against the output. (at least for most SPS).
The best methods that I have seen to actually measure true water flow is to place small squares of disolvable materials througout the tank for a specified time and then measure how much of each one disolved. Flow in most reefs runs about 2 ft per second but this is 2 ft per second over the entire reef, not just the part in front of a pipe outlet.
I think the propeller pumps are a big start in the right direction with a large cone shaped output that creates a lot of flow with limited velocities.
I'll try to find some of my old links on the subject.
FWIW, Nathan
Thanks, Nathan. Nice reef (and house for that matter!) by the way. The concept of low velocity, high volume of water does make sense. I don't quite understand the use of disolvable materials to measure flow that you described, but that may get to be a little too technical for me! :wink:
npaden":fsfi1iea said:
Nathan,
Not to nitpick, but this is an old, old, old method, and it is better at measuring turbulence than velocity... Dissolution rates are not good at telling us velocity.
There are ways to figure these out, but most methods are beyond a normal hobbyist's means. And even these get faked out by really turbulent flows.
In the end, I would just eyeball it, or set up a digital video cam and do some time lapse series to measure the flow frame by frame.
Regards.
Mike Kirda
Why not simply use a stopwatch and time how long a visable particle takes to make it down the length of a tank? There by getting a feet covered in a particular number of seconds. This could be a flake of food, a frozen brine or mysis shrimp etc.. Assuming your fish don't eat them too fast! Other particles work as well. This process has worked well for me when fine tuning the flow within our systems. HTH.
mzem
mzem
Sponsor Reefs
We're a FREE website, and we exist because of hobbyists like YOU who help us run this community.
Click here to sponsor $10:
