Where are my nitrates going?

If the "burn" holes are on older leaves, it sounds like K deficiency. What I'm wondering is, if your plants need K, will they take up the entire KNO3 molecule, use the K and store the NO3 or will they use the K and leave the NO3 if they don't need it?

 

When salts dissolve in water they exist not as molecules, but as free ions, so KNO3 would be K+ and NO3- ions. That tells me the plants can take either or both ions as they need them.

 

Hi,
Plants aren't concerned about low CO2 if there is low light. You mentioned that you discontinued CO2 and reduced nutrients but did you also reduce the light? If so, to what level. If not reduced sufficiently then they are still being driven to uptake CO2 and nutrients and are failing as a result. Additionally, if you are adding sufficient KNO3 and KH2PO4 for their N and P content then you are automatically adding enough K.

Isn't it weird how one day your nitrate test kit returns a zero reading and another day it returns a non-zero reading? At some point one has to realize that NO3/PO4 test kits merrily lead you down the primrose path. First it tells you that you need nitrate so you add nitrate. Then it tells you there's enough nitrate so you add something else. The next step in the illusion is to rationalize or justify why it read low one day and read OK the next.

I'm guessing that you have too much light. This drives a certain CO2 uptake which can't be met by ambient conditions alone. I have empirical evidence that you ought to be able to shut off the lights and leave them off, with the tank only receiving subdued ambient lighting and that the plants would recover more quickly. This sounds absurd, I know, but here is my evidence:

Below is my "nutrient deprivation chamber". This is where I throw clippings, algae victims and other unwanted cast-offs. The basin is in the laundry room barely lit by a side window. These victims stay in the sink until someone else wants them or until they rot, whichever comes first. There's very little CO2, no nutrients except what's in the tap (or supplied by decayed victims) and no circulation. This basin goes completely ignored and unattended for weeks on end yet, many of these clippings have recovered and are doing better in here than in my tank. Look how bright green th P. Stellata sprigs are. There is also no algae. Now, why is this? My conclusion is that the very low light significantly reduces the uptake demand and therefore significantly reduces the stress of high growth demand when in the presence of inadequate CO2 and nutrients.

Now, I suppose I could test the water for NO3 and PO4 but what would the results tell me? Nothing more that what anyone can see in the photo. That whatever concentration level is in the water is good enough for the level of light and the current environmental conditions in the basin.

As bizarre and counterintuitive as it may seem, lowering your light may prove the best medicine.

Cheers,

 

38 watts for 32 gallons will necessarily mean very slow plant growth, no matter how much fertilizer and CO2 you add. If you just about double that light you can then use EI fertilizing rates and the CO2 will be necessary. Light determines the growth rate of plants, assuming adequate fertilizing.