Flow - enough is never enough

[wayne]

Often people underestimate how much flow is required in a marine tank, or rather they never get to see the benfits of adequate flow as they are scared of overdoing it.

Don't get me wrong, there are some fish out there (seahorses for example) and sessile organisms and plants that do better without seemingly brutal amounts of flow. For things such as lps you can cut the flow, or place them in sheltered locations in your hopefully admirally aquascaped tank ( that does not look like a fruit stall) with plenty of features to create sheltered areas.

However for many organisms a whole load of water movement is not going to hurt, and for some things it is a positive advantage. For instance if your interestes extend to tangs, anthias, fairy wrasses, chromis and plenty of other fish, and the obvious suspects for sessiles (SPS< zoanthids, colonial polyps, clams and so on) these organisms are used to, and can deal with flow that when diving will be a positive menace. I have seen some pretty stern currents when diving, but have never felt the current in my aquarium is likely to kill me! Most organisms are caught from shallowish water in what are considered medium flow (6 - 20 cms per second) enviroments. If you've seen a high flow enviroment you will realise it is not practical to hope to reproduce this in the home aquarium ( up to 1 metre per second velocity)

Right now in my tank I'm up to approx. 50 times per hour turnover. This seems a lot, but my stock of pretty ordinary fish seems to handle it pretty well. Some fish still swim in open water, my wrasse, angels and clowns still stick close to structure.

What I'm saying is be sensible, you don't want a washing machine effect, but don't be scared of having your fish or inverts swept away and destroyed.

What that means is that rather than having one great big parallel flow organise your flow so it becomes turbulent and changing, rolling. Point powerheads to cross flow. Use 'propellor' style pumps rather than traditional powerheads if you can get/afford them. Split and direct the flow from your return pump, again to cross, interfere and bounce against other flow sources. With these new, high flow pumps (that are at the same time gentler, but carry further) it is now possible to really get to grips with wave maker machines - mine varys the flow from my main pump between 2500 and 5000 litres per hour on a 20 second basis. Previously some people considered wavemakers a p.i.t.a. as they were very limiting on pump efficiency - this is no longer the case. My flow is deliberately bounced off and around a rock pillar to improve turbulence.


The benefits of high flow are many. Better oxygenation. Better supply of food to sessile inverts. Excercise for your lazy fish. For me the favourite is that I believe it helpes with your filtration. By not allowing debris to settle it is more available for removal by mechanical means (inc. a skimmer), and less available as an algae fuel - one of the killer problems with hair algae is it traps debris - not any more. Also increased flow across your now debris fre LR will allow 'normal' fltration involving the nitrogen cycle to proceed better.

[OCCFan023]

nice thread Wayne, very informative

[Mushroomman]

Very good read

Now this might be too off topic but I have a question regarding "fruit stall" displays. Does anyone happen to have a picture of an example of this? I understand its when corals, rock, etc are just piled in random places and theres no real order but can I get some examples? (feel the definition is a bit un-informative) Id appriciate it.

[RockingCricket]

I read the fruit stall effect as meaning a pyramid style of aquascaping (like a pile of apples) devoid of caves and interest and such like.

I have all (3) of my powerheads gathered in the same corner of the tank, around the HOB inlet to the sump for aesthetic reasons (afterall, thats why I have a sump) and all pointing in the same direction. Pointing them in different directions meant that a film accumulated on the surface of the water because all flow was away from the skimming sump inlet. The only way I found to overcome this without spreading the powerheads around the tank was to point them in the same direction and cause a circular current.
Good to know that many fish can handle stronger currents.

[1979camaro]

i have stickied this

[KahluaZzZ]

Very kind of you

[wayne]

Frankly many tanks are 'fruit stalls'. Rocking cricket has got the idea, but many of them just like a pile or a wall of equally shaped roundish boulders needly stacked together just so, and then to really cap it off a nice selection of small frags spattered across the rockwall, one every 3 inches. This has no shape, no featuring to disrupt flow and create turbulence. Many so called 'tank of the nonths' unfortunately suffer from this, but creme de la creme tanks usually avoid it.

If you had a HOB overflow I can't see how you can have a film accumulating on the surface unless your overflow is a little too deep in the water and it never gets pulled down.

[RockingCricket]

Originally Posted by wayne

If you had a HOB overflow I can't see how you can have a film accumulating on the surface unless your overflow is a little too deep in the water and it never gets pulled down.

Well, it accumulates because the power heads are mounted on and blowing away from the overflow inlet. Therefore the water at my tanks surface is always being pushed away from the overflow inlet and with that any floating particles are pushed to the other end of the tank and held there. As I said the only way I can release them, and keep the powerheads where they are, is to cause a circular (washing machine) current.

[wayne]

Well move the powerheads? Or is there a cabling issue or similar.

[RockingCricket]

Not a cabling issue, just an aesthetic one because I have my tank dividing my lounge and dining room, with the tanks side against the wall so that it can be veiwed from the front or from the back (if that makes sense). It's sticking out from the wll instead of being flat agaisnt it as is traditional. Therefor if the powerheads are anywhere but near the side of the tank near the wall, they are very noticable.
The current powerhead placement seems to be working okay. If there is a washing machine effect, it doesn't appear to be bothering anyone and there don't appear to be any dead spots. I don't want to clog up this sticky any further, but can I confirm how do you identify dead current spots? I am assuming they are highlighted by an area where uneaten food and junk accumulate?