Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
KNO3 supplies nitrogen and potassium.
If you do not dose anything, what does the nitrate level do between water changes?
a) Rises- Do not dose any of this.
b) Stays stable, between 5-20ppm- Maybe dose a low level.
c) Drops- Dose enough to make the NO3 hold steady between 10-20 ppm.
K2SO4 supplies potassium. This is a good material to balance the potassium from KNO3.
a) If the fish food is making the NO3 rise so much you do not have to dose any KNO3, then I would dose plenty of K2SO4.
b) If there is some NO3, but you also have to dose some, then I would also dose some K2SO4 for additional potassium
c) If you have to dose a lot of KNO3, then that might supply enough potassium. Don't also dose K2SO4.
MgSO4 is Epsom salt. Test the General Hardness. If the GH is over 3 German degrees of hardness, then there is likely enough Mg in the water for the plants.
Plants need more calcium than they do magnesium, so unless you know the tap water is unusual, with plenty of calcium, but seriously lacking magnesium (an odd condition, but not impossible) then do not dose Mg without also dosing Ca. If you need both (low GH) then use a complete GH booster such as Seachem Equilibrium or Barr's GH booster.
Chelated micros- Some people find these blends are a bit low in iron, but start out with this one, and lets see what happens.
Your list is lacking phosphorus. This is one of the macro nutrients. If your NO3 is staying high because of fish food, then the phosphorus is probably just fine, too. But if you need to dose KNO3, then you will also need a phosphorus source such as KH2PO4. This is dosed at a fairly low level, so the potassium almost does not count, but the phosphate is very important.
Since you are using CO2, and have fairly high light then you should be dosing a fairly high level of fertilizer. In this setting, the plants are probably using up all the nutrients from fish food, and will be deficient if you do not dose.
The dosing I am most familiar with is the Estimative Index. This is a starting point for a luxury amount of nutrients, which you can adjust as you go forward and see how the plants and the test results are going.
Here is the EI recipe for a smaller tank than yours. I would multiply these amounts by 6 to start with, and try it for a week or two. Note that this method calls for large water changes. If this size water change (50%) is more than you want to do, then just do this amount for 1 week, then test. Lets see what change it has made to the levels. Test with all the tests you have before you start, then test right before a water change.
50% H20 change-weekly
1/2 Tsp-KN03 3x a week
1/8 Tsp-KH2P04 3x a week
3/4 Tsp-GH booster once a week (if needed)
10ml or 1/8Tsp-Trace 3x a week (you can dose more-
2-4ml-Fe/Iron 3x a week
Multiply by 6, and correct a few numbers
50% H20 change-weekly
3 Tsp-KN03 3x a week
3/4 Tsp-KH2P04 3x a week
GH booster once a week (as needed. If needed at all, may be added during the water change)
1 Tsp-Trace 3x a week
Fe/Iron 3x a week (Dose depends on the product you are using)