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Insufficient, fluctuating or poor distribution of CO2 are nearly always at the root of algae issues in high light planted tanks, but measuring it can often be problematic and misleading. There are 3 common methods used for calculating CO2 levels.
The most common method for measuring CO2 is by using the KH/pH tables. These can give false results especially if you have any wood in your tank. The results will tend to suggest that you have higher levels of CO2 than actual levels. This is why you often see people having in excess of 100ppm CO2.
The one ph drop method involves leaving a cup of tank water standing for 24 hours. If the pH of the tank water is one point lower than the water in the cup then it is said you have 30ppm CO2. This does presume that you have 3ppm CO2 in the cup of tank water which very rarely is the case.
The drop checker method uses a drop checker with a KH4 reference solution and a couple of drops of bromo blue pH solution. When the colour is green, CO2 is good, blue too low and yellow is too high. I like this method and use it as an early warning system on my tank, but it does require getting used to the colour changes.
|If your CO2 is turned off at night then turn it on about 2 hours before lights on. You want CO2 levels to be at optimum levels when the lights are turned on. Check levels to make sure that they are good and compare morning to evening figures. You need to have stable CO2 levels through the whole of the lighting period.
Also of high importance to help prevent algae is having a good flow of water around the whole tank. As a guide try to aim for 10x or more the rated filter flow rate to tank size. The idea of this is to provide a constant supply of CO2 and nutrients to the plants by having them move across the leave's surfaces. If you can see all you plants gently swaying then your flow should be good.
Seachem Flourish Excel and Easylife Easy Carbo can be used to fight algae issues and they do seem to work very well against certain types. You can either dose as instructions or two to three times overdose for about two weeks to hit the algae hard. They mainly kill BBA, but also can have an effect on cladophora, staghorn and hair algae. They do affect some plants though. The ones I'm aware of are Egeria Densa, Riccia, Vallis and Fissidens. Some people also report it affecting shrimp and ottos. Another trick is to mix 1 part Excel or Easy Carbo to 3 parts water and add to a sprayer. Do a large water change and whilst the water level is low spray the exposed algae. Leave for 5 to 10 minutes and then fill up with water.