While I agree that you May have a nutrient deficiency I would delay order another fertilizer until we do a little more digging. Let me explain:
Plants need macro and micro nutrients in the water for them to grow:
- Macro nutrients are Nitrogen (N), Phosphorous (P), Potassium (K), Calcium (Ca), Sulfur (S), And Magnesium (Mg)
- Micro (trace) nutrients are Boron(B), Chlorine(Cl), Manganese (Mn), Zinc (Zn), Copper (Cu), moybdenum (Mo) Nickel (Ni), and Cobalt (Co)
I have found it very helpful to assume your water has none of these in it. This assumption is certainly true if you are using distilled, RO, or have very soft water. It is also possible to have deficiencies in soft to medium hardness water.
Look at the Nilog labels:
- The Macro fertilizer has Nitrogen and phosphorous. Ca,S,Mg are not listed.
- The Micro fertilizer has B, Mn, Zn, Cu, Mo. Ni, Co, and Clare not listed. The bottle does list Mg and GH.
The Nilog fertilizer ingredients list is typical of 90% of all fertilizers on the market. Most fertilizers are typically sold to farmers and gardeners. Soil typically has Ca, S, Mg,Ni, Co, and Cl. But putting soil in any aquarium is not a long term solution since soils typically leach out all there nutrients in about a year.
I am glad Dutch is doing OK with it. But that likely means he has the missing ingredients in his tap water. Not all tap waters are nutrient rich. Some are nutrient poor. This simple fact explains why some people have no problem growing plants without fertilizer while others have a lot of problems.
Note I have looked at EI fertilizers and at pressent I have not found any that have Ni, Co, CL. and some are significantly worse than I have lister here.
Seachem flourish, isn't a good brand period.
If you look at the Seachem Flourish comprehensive fertilizer you will find it is deficient in only 1 nutrient (Ni). Seachem Flourish comprehensive works for most people because it is one of 2 fertilizers that I know of that cover almost every nutrient. Note, Nickel was added to the nutrient list only about 30 years ago. Apparently Seachem has not updated there formula. Also Seachem deliberately reduced NPK levels in there fertilizer because most tanks have these in abundance (from fish food). If you have good growth with Seachem you might be shorts a macro nutrient.
The one other notable fertilizer is Brightwell Aquatics Florinmulti. It covers all nutrients except N and P. They designed there fertilizer with the asumption the user would adjust N and P as required by their tank.
https://www.amazon.com/dp/B001LUJLAS/?tag=ff0d01-20
This exercise points to
one possible deficiency, Nickel. However that said plant nutrient uptake can very significantly from plant to plant. So it is possible that plant growth has depleted something in the water and fertilizer. Do you know what your GH and KH, PH numbers are? Also what are your Ammonia, Nitrite, nitrate number That may help pinpoint a cause.