This is what separates a seasoned hobbyist from the newbies. Over a period of time, the question is not whether a reef tank will experience some difficulty, it is only a question of when it will occur and what type of form it will take. Many people abandon the hobby due to the frustration that these obstacles can present, especially early in their hobby experience, so it is critical to identify and resolve these problems before they get to that point.

The most common thing to go wrong is to have the ecological balance of the system get out of balance resulting in rampant growth of obnoxious algae in the system. Besides being cosmetically unacceptable, this can choke out the desirable specimens in the tank.

The system can also go into a state of general decline and malaise where most or all the coral can decline in health or die off.

Fish can become infected with Ick or one of the other saltwater parasites or diseases.

Hair algae (Derbesia)

Description: Hair algae is composed of long dark green filamentous strands up to several inches long.  Hair algae usually starts out in clumps, but can spread into large smothering sheets. The algae mass seems to be detrimental to corals. In some cases, it can smother the coral directly, in others, the algae presence seems to cause recession of the coral through chemical or other means. Once recession starts, the hair algae takes the opportunity to invade the newly exposed skeleton area of the coral. 

Hair algae is probably the most common and toughest problem to overcome. It is definitely easiest to fight hair algae when it first starts before it gets a strong foot hold. The growth of hair algae is generally attributed to there being excessive amounts of nutrients in the water, usually in the form of nitrates or phosphates, although this does not always seem to be the case.

Cyanobacteria

Cyanobacteria looks like a smothering red algae, which coats gravel, rock and reef specimens.

Good water flow and low nutrients seems to help keep this pest in check.  If not, there is a controversial measure that can be taken as shown below.  I recommend using this method only if the situation is getting completely out of control since it can possibly have an adverse affect on the tank bacterial population.

This treatment method includes using an antibacterial medicine such as Erythromycin. Tablets are readily available through your local pet store. I have successfully treated a 29 gallon reef by putting one 200mg. tablet into the sump (remove the carbon during treatment). This cured the problem within about 3 days. I have treated a 20 gallon tank using ½ tablet.

It is important to remove any carbon and stop skimming during the treatment period to prevent premature removal of the antibiotics from the system and to prevent the skimmer from overflowing.

As with antibiotics in general, they should be used only when really needed. Over use can suppress the normal bacterial processes within the tank, and possibly result in creating a strain of cyanobacteria that is resistant to the antibiotic.  In both cases that I used this measure, I did not detect any negative affects on the tank.

Diatoms show up as brown or tan spots on the glass of the tank and on the rocks which are hard to remove. They also show up as a tan or pink ‘jelly’ looking coating on sand and rocks. Diatoms require silica in the water to proliferate.

Best cure for diatoms is prevention.  Usage of replacement water that is silicate free will help to minimize diatom grow, but may not prevent it totally as silicates can enter the tank through foods, etc.  In high silicate water areas, it is probably necessary to use a RO/DI unit to remove the silicates and not just an RO unit.

Treatment includes removal of silicates in the water. The product Phosgard can remove silicates (as well as phosphates) from the tank water.  I have successfully treated a 70 gallon reef by putting a cup of Phosgard into a filter bag in the sump and then replace it with a new cup of Phosgard in 3 days. Within about 5 days, the diatom problem was pretty much resolved.  Phosgard will tend to pull out the phosphates first, so several applications over a couple of weeks may be needed to resolve the issue.

It is normal to get a light dusting of algae on the glass.  How quickly it builds up will depend upon several factors including lighting levels, number of herbivores, nutrient levels in the tank.  Most tanks require a cleaning every couple of days to keep the glass completely clean.  If you have to clean every day, that may be an indication that the nutrient levels are too high.  Again, Phosgard my help if phosphate is causing the excessive growth.

I have successfully reduced the problem from a fairly noticeable coating which needed to be cleaned every day to a light dusting requiring cleaning about twice a week. Used about a cup of Phosgard in a 70 gallon tank which was changed in about 3 days. Algae appeared to be pretty much under control within a week.