A dead spot is an area inside your display aquarium with insufficient water flow. This results in a collection of detritus, poor nutrient export, and minimal gas exchange in that particular area of the tank which ultimately affects the overall health of the aquarium. 

If dead spots are left alone, the build-up of waste will lead to elevated nutrients, algae outbreaks, and possibly even a tank crash due to instability of the microbiome (bacterial foundation). Dead spots most often form because of rocks, corals, or some other obstruction that deflects water flow around that particular area but can also be as simple as not understanding how to properly use your powerheads. In a saltwater aquarium, having sufficient flow throughout the entire display aquarium is pivotal to your success.  

How to Identify a Dead Spot

A dead spot is anywhere where the flow is insufficient for the removal of detritus.  You will notice a collection of debris that keeps growing over time and a general lack of water flow to that area.  Sometimes dead spots occur in easy-to-clean areas of the tank while other times they can be quite pesky and form behind your aquascape or in locations that you cannot easily keep clean with a siphon. It is those pesky, hard-to-reach dead spots that cause the most trouble. 

Dead spot in a reef aquarium

How to Prevent Dead Spots

When setting up your aquarium, there are three major factors to consider that will help you reduce the risk of creating dead spots in the aquarium. Every tank is different and the placement of powerheads and corals on your aquascape will vary from the next tank, all of which come into play when reducing your chances of dead spots. 

Aquascape

Build an aquascape that takes into consideration the placement of your powerheads and will allow for ample water flow around and through the rocks. Don't place rocks directly in front of the pump or build a giant wall that obstructs water flow from reaching the bottom corners. Leave space on all four sides of your aquascape to allow water flow.
Coral Placement

Place your corals logically so they are not obstructing flow while also receiving the right amount of water flow for optimal health.  As corals grow, they may need to be moved or fragged to prevent the creation of dead spots.
Wavemakers/Powerheads

The qty, size, and type of wavemakers you choose to use inside your display aquarium are critical for achieving appropriate internal flow. There are different types of powerheads that produce different flow patterns. Choose pumps that compliment your aquascape and place them in such a way that you are allowing for maximum flow.

 

How to Correct a Dead Spot

  1. Manual Removal - The most effective way to reduce the negative effects of a dead spot is to remove the collected detritus on a weekly basis.  This will keep the area clean and you won't need to add any pumps or switch things up in the display. 
  2. Add a Powerhead - A small inexpensive powerhead just like a Maxi-Jet can target a small area and effectively eliminate a problematic dead spot.
  3. Change Up Flow Pattern - Using your existing powerheads, change the flow pattern by moving the pumps or angling them differently.  Changing flow patterns can stress your corals so be mindful before making drastic changes. 
  4. Move Corals - As corals grow, they can create dead spots.  Fragging or moving larger corals can help reduce dead zones.
  5. Build a New Aquascape - Sometimes aquascapes are simply problematic. If you are having trouble with dead spots or simply don't like your scape, it is possible to tear it down and build a new one without having to re-cycle the aquarium.