[mrhasan]

Originally Posted by Myka

I can't find a flow chart for that powerhead, and I've never actually seen one before, but using some simple math if the flow is 1130 gph at 12V and 3400 gph at 24V then I assume it must be around 1600 gph at 18V. There is probably a bell curve, but this is my closest guess. If indeed there is only 1600 gph and that is the only powerhead in the tank then there is about 24x turnover. That is reasonable, but certainly not high enough to assume you have enough flow. "Plenty of flow" is not necessarily a number value either - observation of inhabitants is your best bet. Brown Jelly would certainly make me take a look at flow first and foremost. Another thought would be chemical warfare.

A single powerhead also creates a lot of dead spots, and certainly lots of variable flow strength within the system. It's tough to run a reef tank with only one powerhead, personally I would want two in a tank that size to better get more consistent flow throughout.

Here's a video for you to judge the flow:

http://www.youtube.com/watch?v=SVvMkrpOfgE