[Wet Thumb Forum]-Low NO3 levels

[Drax7]

I set up a 125 gallon tank last July with sand over topsoil for the substrate and 100W of fluorescent light. I was hoping to follow Diana's method.

My big problem is that my NO3 levels keep winding up at around 0.2 ppm. Wheneven I let them get this low my tank is overrun with all sorts of algae - green water, BBA, green spot, green hair, BGA, cladophora, and brown algae all growing simultaneously!

I've tried feeding tons of food and it doesn't seem to help. The only solution I've found is to add about 1/2 teaspoon of KNO3 a week (divided into small doses throughout the week). As long as I do this, the water stays clear and the algae stays pretty much in check.

Two questions: 1) What am I doing wrong? 2) Is there any long-term bad effects to adding KNO3?



- Jim</p>

[Drax7]

I set up a 125 gallon tank last July with sand over topsoil for the substrate and 100W of fluorescent light. I was hoping to follow Diana's method.

My big problem is that my NO3 levels keep winding up at around 0.2 ppm. Wheneven I let them get this low my tank is overrun with all sorts of algae - green water, BBA, green spot, green hair, BGA, cladophora, and brown algae all growing simultaneously!

I've tried feeding tons of food and it doesn't seem to help. The only solution I've found is to add about 1/2 teaspoon of KNO3 a week (divided into small doses throughout the week). As long as I do this, the water stays clear and the algae stays pretty much in check.

Two questions: 1) What am I doing wrong? 2) Is there any long-term bad effects to adding KNO3?



- Jim</p>

[dwalstad]

It sounds like you're doing everything right!

There should not be a bad effect from adding KNO3. It could be that your plants need more potassium (the K in the KNO3). My fishfood analysis (p. 88 in my book) shows fishfood provides 3.3 times more nitrogen than K. If your tank is low in N, then it could be VERY low in K.

If your tank water is soft or borderline soft, then it doesn't begin with enough potassium. Hardwater usually has enough potassium.

When you add KNO3, you stimulate plant growth by giving them a very important nutrient (potassium). The stimulated plant growth may keep the algae in check. I see nothing wrong with adding KNO3 in the amounts you describe.

If your water is soft (GH less than , you might want to increase your water hardness so that plants also get enough calcium and magnesium.

Diana Walstad

[Drax7]

Thanks for the reply, Diana.

Actually, the water is quite hard, with a GH of 12 the last time I measured it.

I was assuming that N, rather than K, was limiting. After all, a level of 0.2 ppm NO3 seems awfully low. With my additions it stays around 5 ppm NO3.

If plant growth tapers off I'll try adding some KCl and see if that perks things back up. For now things seem to be OK with just the KNO3.

Thanks again.



- Jim</p>

[dwalstad]

That's interesting what you wrote. If you decide to try KCl instead of KNO3, let us know what happens!

Diana Walstad