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Please can I have some help. I am running a 500-litre planted aquarium, predominantly young Discus with Sterbai Corydoras, Peppermint Bristlenose and L333 Plecos. I am feeding heavily (in order to grow the young discus), perform 30% water changes every 3 days, my tank is sparkling with pH at 6.6, Ammonia at 0.0ppm, Nitrites at 0.0ppm and Nitrates at 10.00-12.50ppm before water changes. I vacuum during the WCs and the tank and fish all look fantastic. My lights are on for a total of 8 hours a day, 3 hours in the morning and 5 hours in the evening. We live in a unit and the tank is located in the lounge where there are no curtains with massive glass doors/windows and although the tank does not get direct sunlight the lounge is very bright so even when the lights are off the tank gets plenty of natural light.

My problem, as can be seen from the attached photographs is that algae is growing on my plants. Previously I had lights on for 13 hours a day and had a similar problem, I dipped all plants in bleach, removed the affected leaves and reduced the light to the abovementioned 8 hours. Within 10 days the algae has returned. The only other algae I have are hard green spots on the glass and some light algae on the glass, I am able to remove all algae from the glass with a magnet algae scrubber, the green spots require a bit of hard work.

I have reviewed this problem extensively online and think that I may have a phosphate problem in my tank. I do not own a phosphate test kit so can not confirm this. My thoughts are that I should purchase a phosphate test kit and if my phosphates are high place Seachem PhosGuard in my Fluval FX6 canister filter. This is all new to me, is my suggested course of action the correct way to go or should I try a different course of action? Any suggestions would be gratefully appreciated.

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Correct. This might help...

What do all algae (and cyano too) need to survive? Nutrients. What are nutrients? Ammonia/ammonium, nitrite, nitrate, phosphate and urea are the major ones. Which ones cause most of the algae in your tank? These same ones. Why can't you just remove these nutrients and eliminate all the algae in your tank? Because these nutrients are the result of the animals you keep.

So how do your animals "make" these nutrients? Well a large part the nutrients comes from pee (urea). Pee is very high in urea and ammonia, and these are a favorite food of algae and some bacteria. This is why your glass will always need cleaning; because the pee hits the glass before anything else, and algae on the glass consume the ammonia and urea immediately (using photosynthesis) and grow more. In the ocean and lakes, phytoplankton consume the ammonia and urea in open water, and seaweed consume it in shallow areas, but in a tank you don't have enough space or water volume for this, and, your other filters or animals often remove or kill the phytoplankton or seaweed anyway. So, the nutrients stay in your tank.

Then, the ammonia/ammonium hits your rocks, and the periphyton on the rocks consumes more ammonia and urea. Periphyton is both algae and animals, and is the reason your rocks change color after a few weeks from when they were new. Then the ammonia goes inside the rock, or hits your sand, and bacteria there convert it into nitrite and nitrate. However, the nutrients are still in your tank.

Also let's not forget phosphate, which comes from solid organic food particles. When these particles are eaten by microbes and clean up crews, the organic phosphorus in them is converted into phosphate. However, the nutrients are still in your tank.

So whenever you have algae or cyano "problems", you simply have not exported enough nutrients out of your tank compared to how much you have been feeding (note: live rock can absorb phosphate for up to a year, making it seem like there was never a problem. Then after a year, there is a problem). 

So just increase your nutrient exports. You could also reduce feeding, and this has the same effect, but it's certainly not fun when you want to feed your animals :)
 

 

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