Macro Algae

10 Sep 2007
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Micro algae grow as a result of either of two nutrients being in the water in too large a quantity:

1. green micros grow when there is too much phosphate in the tank water

2. brown micros grow when there is too much silicate in the tank water

Both can come from internal and external sources,they can be either generated inside the tank itself or they are added by the hobbyist ,

When these nutrients are high, micro algae grow, and harvesting them does not solve the problem

What happens when you do this is that you remove a quantity of algae but you kill off a number of them too that are not removed.

When dead algae start to decompose they add phosphate and silicate to the tank, depending on the kind.
This process then leads to the growth of more algae since the basic building blocks for growth (Phosphate and Silicate) are there.

This can be baffling as you keep pulling algae out and as fast as you pull them out other ones grow.

The reason is that when you pull these algae out you also contribute to the increase of PO4 and silicate as explained and that makes more of them grow.

There are some ways to deal with this :

1. Eliminate all outside sources of phosphate and silicate and make sure you do not add any to the tank. To do this you need to check the water you use for them, the salt, the additives, the carbon (often leaches phosphates) and so on. Eliminate anything that adds nutrients to the water by switching to another brand or if it is the water by treating it and removing the phosphate and silicate

2. Eliminate or minimize internal sources: clean up detritus you see, remove uneaten food, do not overstock the tank, do not overfeed, put algae eating fish in the tank are examples of what you can do.

3. Water changes with water that not contain PO4 and silicate will help you lower their levels. When the levels go down algae start to die off. Siphon those out. Do not let them die off in the tank or you will again contribute more nutrients which will result in more algal growth.

4. Use compounds that remove PO4 and SiO2 to lower the levels even further.

5. Use Hermit crabs

6. Perform water changes if the levels are real high right now to lower the ppm concentrations

Read up on algae and on how to use the products that reduce PO4 and silicate and you will get the problem under control.

Do not scrape algae off the glass as that just kills them and adds more PO4 to the tank (or silicate is the algae are brown which means they are diatoms).
Use a sponge and wipe from bottom to top, then rinse the sponge, then go to the next area and wipe from bottom to top, rinse, etc. Keep doing this until all panels are clean. Doing it in this manner you won't introduce algae in the water and thus lower the amount of PO4,Silicate added to the water when they die off.

When you have the levels real low and no algae grow you can use the addition of kalkwasser to the tank to control phosphates.


Retired Moderator
29 May 2007
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Cape Town
Mekaeel - I am not an expert - BUT, ONLY kalkwasser WITH nutrients in it in the FIRST place, can raise nutrients....
Nutrients can only exist because of organic matter being "broken down" to it's lowest form....

If there's no organic matter, then there cannot be any nutrients - so - what kalkwasser will contain organic matter?

I am QUITE sure mine doesn't....
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