What Ppm To Shoot For When The Nutrient Is In My Water Source?


New Member
Oct 26, 2018
For low tech with no CO2, btw.

I'm using Zorfox on custom solution. My bottles are 500ml and each pump doses 2ml. At the tank size of 10 gallons (so a pump per every 10 gallons.) About 1-2x a week on low to medium light. No fancy PAR rated lights, just generic LED floods or shop lights or bulbs.

I was advised to leave the PPM as it automatically is, which is 7.75ppm.

Calculations are as follows: "Add 115.729695699 gm of KNO3 to your 500 ML container. Each dose of 2 ML will raise NO3 7.5 ppm in your 10 gallon tank tank."

BUT I already have nitrates in my water supply. 7.77 PPM. And I also have wood and dead leaves that I add.

So should I not be adding any additional KNO3 at all? Unless I don't do a water change every week? I have algae problems absolutely no matter what I do and no matter how little light I use. Even without any fertilizers.

I typically do a water change every few weeks on most of my tanks, because I really understock and over filtrate. I have a range of sizes, but most are 55 gallons right now, with a few small cichlids, two over rated filters (one HOB, the other a sponge), and pool filter sand substrate in most of them. Not dirty tanks, so not tons of fish waste.

So if I shouldn't add any KNO3 when I do a water change, but should if I don't do a water change, and the KNO3 gets used up and I need more by then, doesn't that mean I'd need like two sets of Macros mixed up for these two separate doses??

I have a big bag of KNO3 and another big bag of KH2PO4. No separate Potassium. (If this is even relevant.)

calvin doss

Lifetime Member
Lifetime Member
Jun 22, 2020
Washington State
Dear CaptMicha,

The potassium is relevant. If you do not put in the KNO3, you will need a different potassium source. The macros are N,P,K - K is potassium.

If you have some GH booster or Equalibrium, that has some potassium. If you have those, then you might add that to your water and cut in half the KNO3.

I am not the algae expert, but this site indicates that having excess NO3 is not so relevant in this case. However, any amount of excess NH3 (ammonia) would produce algae. The nitrogen in the form of NH3 is an algae trigger. I would be concerned that the decomposition of the leaves would produce NH3 in the breakdown process.

By the way, this is not advice. These are my thoughts. I am not suggesting you change what you are doing.

Best of luck!