No chemicals, fast results.
Once I put some fertilizer tabs in my planted fresh water fish tank, the green algae started growing and in a matter of days the water was crowded with them. A greenish color, milky water, I couldn’t see through my tank. The plants were also not getting enough light.
I changed about 50% of the water once in 10 days. Tried it twice. This was supposed to clear the algae/nutrients so new algae would not form. Didn’t work. Two days later and I was back to a green water tank.
My solution: paper towels(!).
First I used my small acrylic fry tank, put a double layer paper towel in it and placed it under the filter return. I thought – maybe the kitchen paper towel would be good enough to filter the algae. Result: overnight the water got significantly clearer.
You can see the fry tank padded with the double paper towel right under the filter output. Basically just another filtering stage. (yes, those are superglued ping pong balls to help with the flotation)
As I realized the next morning that the paper towel filtering was working, I updated the process with the intention to get rid of the fry tank. I mounted the paper towel inside the filter, on the intake side of the filtering cartridge. I assume I could have put it on either side, as long as it covered the cartridge surface (view images below).
This filter paper has been sitting in the tank filter for just a few hours (about 5). With both filters in place (fry tank and inside tank filter) the water is almost back to clear in just a few hours. I replaced the main filter paper towel just to get a bit better results.
There are two filter towels in the tank filter: one over the filtration cartridge (main algae filtering purpose) and one in the overflow section.
This is what happens: main filter towel gets clogged fairly easily with algae/other things, as its pores are very small. The water starts rushing through the overflow on the left side instead of going through the main circuit, bypassing the filter. This is why I need the second folded towel to stop the water from going through the overflow and actually directing it through the main filter.
This is how the two towels look like (the one in the fry tank after 20 hours and the one from the main filter after 4-5 hours).
I didn’t use the fry tank anymore, just a paper towel in the main tank filter. I won’t leave it there too long, as it clogs pretty fast and prevents the water flow through the main cartridge. Anyways, used the method, it works excellent, with really fast results.
I don’t know how long it will last until algae will be back to make my tank water green, but this way I am not using any chemicals in the tank (this was my main goal).
It should last for a few days, and then I’ll have to repeat the process – until those plant nutrient tabs are totally gone from the system and won’t help any more algae growth.