Why Are Repeated Po4 Reducing Treatments Required
-The Problem
Frequently hobbyists will send email to various mailing lists requesting information on how to get rid of green undesirable algae, and want to know the exact approach to take to do so.
"What do I need to do to get rid of those slime, hairy, filamentous or filamentatious algae", is the typical question.
The problem is, of course, that over time or for some specific not yet identified reasons, the water in the tank becomes loaded with organic and other forms of phosphate based compounds.
When this happens, these undesirable algae grow and spread rapidly covering everything in the aquarium, unless speedy action is taken to lower these phosphate levels. One is amazed at the speed with which these algae can spread once they start to appear in the aquarium.
The real nutrient for these and other forms of algae and what makes them grown is "ortho-phosphate". This is the mineralized form of any type of phosphate present in the aquarium. Organic phosphates, whether simple or complex ones, break down and mineralize and eventually appear in the aquarium water as ortho-phosphate.
Algae of all sorts thrive on this nutrient and when it is present, rapidly grow and proliferate all over the tank, including on your coralline algae, your coral's skeletons and so on. Not a pretty picture indeed.
-Course of action
In order to solve this problem the approach needs to be two-fold:
-The phosphate already present in the aquarium needs to be removed from the water so algae are starved slowly of nutrients and gradually die off as a result.
-Sources of phosphate need to be identified and eliminated so that the build up does not reoccur. If external sources can be found that artificially add PO4 to the tank, the hobbyist can elininate these.
There are several methods that are generally suggested for the removal of phosphate from aquariums. The easiest one, but not necessarily the least expensive one is to make water changes (a certain percentage of the tank content) every day. The water that is then added to replace this needs to be free of phosphates of course and needs to have the same general water quality parameters as the water already in the tank.
Another method suggested by various authors and manufacturers is the use of phosphate removing compounds. These are usually metal oxides that have been specially treated to absorb ortho-phosphate.
Several brands appear to compete with each other in this area. All would appear to be the same though: aluminium oxide treated in special manners and then agglomerated and sold in powder, granules, chunks, balls and so on (even impregnated pads are available).
Either of these methods will eventually bring the phosphate levels down and prevent algae growh after having allowed you to rid the aquarium of the algae that were already there.
-How to Proceed?
Whichever method you use is not important, as long as you persevere. That appears to be the main key to being successful. You may want to use several methods at the same time.
The amount of phosphate in the aquarium water may be really high and as a result, one or two water changes, or one or two treatments with the compounds mentioned are not going to solve your problem.
You will need to do either of the following:
-Method 1 - Water Changes
Test your phosphate level and make a note of it (day 1)
Perform a 10 percent water change (day 1)
Test your phosphate level and make a note of it (day 1)
Test your phosphate level (day 2 - 24 hours after the first water change)
Change another 10 percent of the tank's water (day 2)
Test your phosphate level after the water change (day 2)
Test your phosphate level (day 3 - 24 hours after the second water change)
Change another 10 percent of the tank's water (day 3)
Test your phosphate level (day 3)
Keep doing so until the phosphate level has dropped and dropped and is in the neighbourhood of 0.03 to 0.04 ppm
As long as it is higher you need to continue to change water.
As you can see this becomes pretty costly because of all the salt needed, the treated water you use, and the tests you perform.
Note that most tests on the market do not test below 0.1 ppm and that even if your phosphate level is 0.06 ppm (which is too high), your test may show that you have zero phosphates (when this is not the case).
The reason for this is simple: your test is not sensitive enough to measure below 0.1 ppm and you will, therefore, not get an accurate result.
As you keep performing water changes though, and unless you introduce phosphate in some manner directly to the tank, the levels should go down and the green undesirable algae that we call micro-algae should start to die off.
It is recommended that you siphon these out of the tank. This prevents them from decaying and adding more phosphate to the water (which would lead to more algae growth).
-Method 2 - PO4 Removing Compounds
This method relies on the use of phosphate removing compounds, the metal oxides refered to earlier.
What is suggested is to place a batch of this compound in the tank and make sure that contact between the compound and the water is high. These compounds work likes sponges thus for them to absorb phospahtes, they need to be in contact with the water or they cannot absorb.
Because such compounds become saturated (they can only absorb a certain quantity of phosphate), it follows that they will need to be replaced.
The higher the level of phosphate is that you start at, the sooner you will need to change them in the beginning as the high levels of phosphate will quickly saturate the compounds.
As the levels diminish you will find that they will remove phosphates for longer because they do not saturate themselves as quickly.
How do you know then when to change the compound. Simply, by testing the water and determining what happens to the concentration of phosphate.
As long as the ppm level keeps going down, the compound is still absorbing phosphates. When the level stays the same or starts to rise again, you need to replace the compound with a fresh batch.
The higher the initial level, the more times you will need to do this. The results of your testing will indicate when you have achieved a low concentration and when you can stop.
Of course, during this treatment period algae will die off, or change color (the green will tend to look less green). Siphon them out to prevent them from breaking down and adding more phosphates to the water (as this would give rise to more algae).
When either all algae have disappeared, or when the phosphate levels are low enough, put in a fresh batch and leave it in the tank so it can absorb whatever phosphate is being produced.
At some point your tank will be free of algae but how many changes of compound this will take is hard to tell as it depends on each individual situation and how much phosphate there was to begin with.
-Method 3 - Hermit Crabs
This is a simple method and relies on adding hermit crabs to the tank as they consume the algae as fast they grow. This is a bit of a patch method since you are dealing with the outcome (growth of algae) and not with the cause (too high levels of phosphate).
How many hermit crabs are needed depends on the size of the tank. I do not know if there actually is a correct way to gauge this. My suggestion is to use about one per 20 liters of water (ed. note: about 5 gallons). This is not necessarily the case for everyone though. Some may need more and some may need less as we shall see.
If that amount of herbivous hermit crabs does not keep the growth under control or eradicate it, you may need to add some more. This can always easily be done as the are so available and inexpensive.
Keep in mind though that as the hermit crabs feed on the algae, the amount of algae diminishes and so does the food for the hermit crabs. There comes a point where the amount of algae in the tank is too small to sustain all the hermit crabs you have placed in your tank!
This can, in my experience, pose a problem and the problem can be quite serious indeed. When not enough food is available in the from of algae, some of these hermit crabs start attacking other animals in the aquarium.
I have experienced this, and seen these hermits attack snails and even in one case I observed, a shrimp.
One of the more general problems sometimes reported is that the hermits crabs attack other animals and are not just herbivorous but may be carnivorous or omnivorous. This may very well have to do with the fact that they are running out of food. Once the algae are eaten, the hermit crabs are still there but there is far less, if any, food for them to consume. What does this bring about?
I suggest that this could lead to predation in the aquarium because not enough food for all those hermit crabs is available (the first victims appear to be snails).
We may, under this method, have to lower the number of hermit crabs of various kinds to prevent this from happening.
-Conclusion
Various methods to lower phosphate levels were described. All have their advantages and disadvantages. Selecting one method over another is probably not the better manner in dealing with phosphate concentration management. More than likely you will want to use a combination of all of these methods to arrive at a water quality that is low in phosphates and prevents undesirable algae from growing.
Some have postulated that phosphate that accumulates in the plenum may find its way back into the aquarium water by osmosis. This is certainly a possibility but I have not seen any evidence of it. If the levels are extremely high then such osmosis could very well take place and plague our tanks with continuous additions of small amounts of phosphate. I guess in this area more will become known as time goes on.
