Ok, noted. How about Mg? My tap water has about 5mg/l. I'm adding Epsom salts (1/2 tsp three times a week to my 120l tank), can I stop that?
As Darrel mentions, you can just carry on adding the MG that you are adding and at some point, try deleting the addition. Mg is also a micro nutrient so you only need microscopic amounts. Epsom salt is most useful for RO and soft water homes when the Mg content is virtually absent.
I wish there were some easy to use guidelines for identifying nutrient deficiencies, but I suppose it's not that simple. A lot of the deficiencies I've seen described for different nutrients look very similar to each other...
Well in almost all cases it is actually very easy.
The troubleshooting procedure is very basic when it comes to aquatic plants, but many hobbyists are fooled into thinking that the symptoms that appear for terrestrial plants are the same under water. They then start to try and decipher the symptoms and they almost always misdiagnose.
Here is an easy summary and procedure that will get you started and will give you a better chance of success.
1. Rule #1 is to ignore any of the deficiency charts you see scattered around the internet that are essentially guides for land plants.
2. By far, the most common deficiency in planted tanks, even in CO2 injected tanks or in tanks using other carbon enrichment methods is ironically, CO2. Melting leaves, distorted leaves, holes in leaves, stunted leaves, browning in leaves or stems, translucency of tissue, brown spots, black spots, disintegrating tissue, falling leaves (especially lower leaves) and any other structural anomalies exhibited
anywhere on the plant is due to a Carbon shortfall. Carbon is the dominant element in plant tissue and therefore any shortfall of this element is immediately revealed as damage, deformation or necrosis of the tissue. Carbon shortages also triggers all forms of filamentous algae, most commonly, Hair Algae. Poor CO2 can trigger Green Spot Algae (GSA), Black Brush Algae (BBA), Cladophora Algae, Green Dust Algae (GDA), Oedogonium Algae, Rhizoclonium Algae and Staghorn Algae.
As you can see, this covers about 90% of the problems you will ever see, so this makes it very easy to diagnose.
How you
fix a Carbon shortage though, is not easy and in fact is the most difficult procedural aspect of planted tanks.
3. Micronutrient shortages are rarely, if ever, the cause of algal blooms and their shortages can easily result in pale or yellowing leaves. Since almost all the micronutrients
first appear as discoloration of YOUNG leaves that makes the diagnosis fairly easy, however, it's not really necessary to know specifically which one is the cause.
To avoid that complication you simply add more of the micronutrient mix(es), which will cover all of them, i.e. Iron, Magnesium, and so forth. Do not try and determine which - just add more of all of them. Too many people waste time and energy attempting precision. This is a useless strategy.
Also, if you are already adding the recommended amount(s) of micronutrients, and yet still experience these symptoms that tells you immediately that either your flow and distribution techniques are at fault or that the tank water is hard and that the chelation being used is failing so that the nutrients precipitate out of solution before getting to the plants. You should be able to see the precipitate though as it will give the water a tinge of yellow, brown or green for a few hours after dosing until the precipitate falls to the ground or is picked up by the filter.
3. Nitrogen shortage are revealed as yellowing or other forms of discoloration of MATURE leaves. The similar diagnosis applies here; if you are adding the prescribed amounts of Nitrogen and if the symptoms appear, then you need to review flow/distribution. No precipitate issues arise in this case.
4. Phosphorous shortage can result in stunting, but most often appears as Green Spot Algae (GSA). As noted in Item 2. GSA can also be caused by CO2 so when examining the tank as a whole look for other symptoms of CO2 shortages so that you can separate PO4 shortage from CO2 shortage. As with the other nutrients, if you are adding the prescribed amounts and still experience the symptoms, then flow/distribution must be reviewed.
5. Potassium shortage is the most difficult to assess as this nutrient is used in almost every function of the plant. So for example Potassium is needed in order for the plant to uptake NO3. Potassium is also responsible for maintaining turgidity and the pH of the cell and tissue between 7 and 8. Outside the acceptable range many plant functions cease. So a shortage may appear as a Nitrogen shortage or may appear as stunting. To get around this complication dose a Potassium based salt for Nitrogen and for Phosphorous such as KNO3 and KH2PO4. This will ensure that there is more than enough K. If using other forms of N, such as Urea or Ammonium Nitrate then ensure that other Potassium salts are added such as KH2SO4.
Hope this helps to simplify because dosing NPK+micros is meant to be the easiest of all things planted.
Also please review the Dropchecker article in the Tutorials section.
Cheers,