Low vs Medium vs High Flow?

[madducks42]

We're slowly starting to add coral to our tank and I'm trying to figure out what people mean exactly when they say "medium flow" or "high flow". We have two Apex WAV powerheads in a 90 gallon tank, they're only running at 1% but I'm concerned that it's still too much flow. I've messed around with their positioning but it seems that no matter where I put them the flow in the tank remains pretty consistent. They're currently on opposite ends of the back wall, angled to point to the side wall and bounce off.

We picked up a small hammer coral over the weekend and I'm trying to find a good spot for it in the tank. This is where we currently have it, it's been in the tank a few days and has opened up quite a bit which makes me think this is an okay spot. But when I see videos of other people's hammer corals they don't seem to be thrashed around as much by the flow.

 

[ndrwater]

I would call that medium flow which is perfect for a Euphillia like your hammer.
Low flow is moving, but barely.
High flow, like the flow SPS generally like, is significantly more that you show in your video.

 

[andrew james]

Use your rock to block flow in places where you plan for lower flow corals like a hammer. Eventually as your tank grows you'll slowly turn up the power to match and move water around bigger colonies

 

[Tautog]

I think you need to attach your power heads to the sides, and direct them to your rear glass wall, thus pushing any debris to the front. Easy cleaning. IMO, more is better, the more flow creating surface movement the better the oxygen exchange will be. It's impossible to have extremely high flow in every part of your tank, but those low flow spots are necessary for some corals. Therefore, in order to have a larger collection of different corals, you will need the high flow heads. Spend once, you will be happy you did, 50-60 X your total gallons.

 

[GoVols]

Even if you have high flow for SPS that does not mean direct flow pounding them. as @Tautog stated. If you take the time to tune in the flow the you can make all your corals happy. If you run too much flow even your sps can get an algae type grow from the water burn from to much direct flow. If your tune your flow your corals will guide you when they are happy.

 

[madducks42]

Thanks for the replies all! Between the return pump and the powerheads I think the overall flow in the tank is really good. I was just concerned that even in places with indirect flow that it was still too much. But if the movement above looks like good medium flow then that helps me figure out the high and medium flow spots or the tank. I'm not sure if we have any spots in the tank that would be considered low flow which we'll have to keep in mind if we want to add anything later on that needs low flow. I think most of what we're interested in would require medium or high flow anyway.

This is where the powerheads are currently. I think I'm pretty happy with the one on the right. I might mess around with the one on the left more. I tried to position them so that they're at least in part hitting the live rock and creating a flow around it. I have a few complaints about these powerheads, lol. One being that even at 1% they're running at 1800rpm, they go up to 4000rpm. But that means at 1% they're running at almost 50% of their potential. The other major problem I have with them is they're not really easy to angle in any direction. I would like to position them a little bit lower and angled up more but even when I have them angled up as much as they can go it's still barely more than straight on : /

Tank:

Left:

Right: