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Filter Floss: When to Replace It for Optimal Aquarium Health

A common question among new aquarium owners is, “How often should I replace my filter floss?”

And one of the most common answers you’ll see on popular reef keeping forums is “every 2 to 3 days”.

There are two slight problems with this rote piece of advice though:

  1. It could cost you extra money. And,
  2. It could starve your tank.

Every tank is unique, including yours. Just because changing the filter floss every 3 days works best on another person’s tank doesn’t mean it will work best for yours.

How often you change your filter floss will depend on your bio-load and the maturity of your tank.

filter floss cut into strips
Filter floss cut into 1 inch strips for placement between sump baffles.

Consider a new tank that is less than three months old…

Changing the filter floss too often could deprive the bacteria and other microscopic critters of the food they need to develop. This may result in your tank taking longer to mature than usual.

Likewise, changing filter floss too often in a established, mature tank could strip the water of too many nutrients causing the coral to starve.

So where does the common ‘2 to 3 days’ come into play?

As a starting point.

Filter floss isn’t needed until you reach your desired nutrient levels. Phosphate of 0.03 ppm and nitrate of 1 to 5 ppm are most typical.

Once your tank is at your desired nutrient levels begin using filter floss.

For the next 4 to 6 weeks replace it every three days.

Be sure to test your phosphates and nitrates at least twice a week during this period.


Let Your Tank ‘Tell’ You When to Change the Filter Floss

If your nutrients continue to rise during the test period switch to replacing it every 2 days – and consider adding additional filtration such as a skimmer and/or granular activated carbon if you don’t already use them.

If your nutrients hold steady or drop closer to zero during the test period, try replacing the filter floss every five days.

Keep testing for 4 to 6 weeks.

If the nutrients continue to hold stable or drop, bump the replacement schedule out to once a week.

Keep testing. And keep bumping the schedule out.

When your nutrients start to rise a little, stop and switch back to the previous schedule. Congratulations! You’ve found your filter floss replacement ‘sweet spot’.

For example, if they were stable when you replaced the floss every 7 days (once a week) but started to rise when you replaced it every 9 days, stop. 7 days is your replacement ‘sweet spot’.

Changing it more often than 7 days would just be wasting money. And waiting longer than 7 days will cause your nutrient levels to rise.

What if your able to go for several weeks without replacing the floss and still see no rise in your nutrient levels?

Well then you may not need to use filter floss at all. It would indicate the other biological and/or mechanical filtration in your system is more than enough to keep your nutrient levels in check.


A Simple DIY Crab Trap for Catching Aquarium Pests

This DIY crab trap is a quick and easy way to remove unwanted nuisance crabs from your aquarium.

Unwanted pests such as gorilla crabs and stone crabs often make their way into aquariums as hitchhikers on live rock.

At first that my not be a problem. They can even serve as a valuable member of a clean-up crew while they’re small. But as they get bigger and their appetites grow, they will often start to eat corals or other more desirable members of your clean-up crew such as porcelain crabs, snails, and even small fish.

Many aquarists will spend hours trying to spear them with a skewer, or a pair of large tweezers. And some will even resort to spending anywhere from $15 to $50 on a pre-made pest trap.

Before you spend that much time or money though, there is an old reef keepers’ trick you might want to try first.

You can make a very simple DIY crab trap using nothing more than a small glass.

Here you can see the quarter-sized stone crab I caught an ordinary shot glass. Two tries with shrimp didn’t work. But it took less than 30 minutes to catch when I used a little bay scallop as bait.

shot glass crab trap
Small stone crab caught in a DIY shot glass crab trap.

A shot glass will work for small crabs that are about the size of a quarter or smaller.  For larger crabs you can use a bigger glass; one that is just tall enough so that the crab can’t reach the lip if it extends its claw.

The only thing you need other than a glass is some bait. Some people have success with a piece or raw shrimp from the grocery store. I tried shrimp twice but didn’t have much luck with it. On the third attempt to catch the little stone crab that was terrorizing my tank, I tried a small piece of raw bay scallop and it worked like a charm.

Simply place the glass in the bottom of your aquarium about 30 minutes before the lights turn off for the night, and lean it at an angle so the lip of the glass is resting against a rock.

Then place a small piece of the bait in the bottom of the glass and let it sit overnight.

The crab will climb down into the glass to eat the bait. But it won’t be able to get back out because the walls of the glass are too smooth for it climb up.

It make take a few tries, but a lot of reef keepers have had great success using this quick and simple DIY crab trap.


Cyanobacteria … or Spirulina algae?

Cyanobacteria is a common occurrence in saltwater aquariums. Aquariums under a year old seem particularly prone to outbreaks.

Cyano is typically red. But it can also be brown, blue-green, or even green.

Regardless of the color, it grows in slimy strands that form  ‘mats’ on the rock and sand.  (To see some great pictures of a typical red cyano out break, check out this page over at Melev’s Reef.)

So, when these green, slimy ‘mats’ began showing up on my rock and then my sand bed a few weeks ago, my first thought was cyanobacteria.

It looked like green cyanobacteria
I thought green-colored cyanobacteria was beginning to cover my ball sponge and sand bed…

However, my online research soon revealed that cyanobacteria has a little-known relative that looks exactly the same to the naked eye: spirulina algae.

And it’s important to know which one you are up against because the methods for treating the two can be quite different.

How can you determine if it’s cyanobacteria or spirulina algae?

Simple, with a few drops of hydrogen peroxide.

Chances are you already have a bottle sitting in your medicine cabinet. If not, you can pick up a regular bottle of 3% hydrogen peroxide at most any grocery store or corner pharmacy.

Simply place a few clumps of the cyano into a container along with 2 cups of water from your aquarium.

Add 1 ml (20 drops) of hydrogen peroxide to it and then let it sit for several hours.

Peroxide is deadly to cyanobacteria. It easily breaks the cyano down and kills it. But peroxide has absolutely NO effect on spirulina algae.


If the water turns the same color as the cyano, it means you are indeed up against cyanobacteria.

If the water remains clear and the ‘cyano’ clumps show absolutely no signs of dissolving, then it is NOT cyanobacteria.

There are several methods you can use to get rid of cyano.

Many aquarists use the old-school method of keeping their tank lights off and the entire room dim for 3 days in order to starve it of light.

In some cases this isn’t enough to do the trick though and the cyano returns a few days after the lights are turned back on.

Others recommend dosing the aquarium with peroxide using a dosage of 1 ml of peroxide for every 10 gallons of water twice per day for 14 days straight.

Mild doses of peroxide have been proven to wipe out cyano while being safe on all other tank inhabitants.

And still others swear by the use of products like ChemiClean and Red Slime Stain Remover.

In fact, Chemiclean will eliminate both cyanobacteria and spirulina.

From what I’ve read, the key to success with products like these is to follow the direction to the tee. That means making sure you oxygenate the water as much as possible with powerheads and/or air stones. And doing the recommended water change as soon as the treatment is complete.

As for me, well, the water in my test stayed clear so it’s not cyano. That means it’s either spirulina or some other form of algae.

I’m going to give my tank a few more weeks to see if regular water changes will lower my nutrient levels enough to both starve it out and bring my good bacteria back into balance with the bad bacteria.

If so, the outbreak I’m experiencing may clear up on it’s own.

If it doesn’t, I’ll probably pay a visit and order some Chemiclean.