Liquid fertilizer and dirt substrate

You can buy Iron (Fe) test kits and monitor iron levels in the aquarium. You want the iron level around 1mg/litre (1ppm) and no higher because higher levels affect fish and other life forms (as mentioned by Byron).

Stan510 said:

This what ive found after 50 years of plant keeping..iron is all you need. If you feed your fish? That and poop provide all the rest- more than enough in fact most of the time. Try just iron. Watch plants thrive.

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it should be noted that Stan besed on his journal doesn't do water changes. He is relying on fish waste to produce most of the nutrients his plants need. However he doesn't get enough iron doing this. Not doing water changes doesn't work for everyone and there are some risks. And in my experience not all water has all 17 nutrients needed for good plant growth. Some people have Distilled or RO water coming out of their taps and that water has zero nutrients in it. S. Repens does very well when it gets all 17 nutrients plats need for growth.

For Martincregg I would recommend fertilizing. Your water changes will wash out some of the nutrients in your soil over time. And eventually the soil will run out and the plants will stop growing. A fertilizer will help to prevent that.

Easy green is as good as any other and it has a very good iron fertilizer in it so I wouldn't expect iron probems with it unless your tap water pH is above 8. However in my experience with trying to make my own fertilizer, KH in your tap water destroys the fertilizer after a short time. Many fertilizers work better is if dosed about every other day or so. You might want to try dividing the recommended dose into about 5 smaller does as a start. If that doesn't work you can then try increasing the amount of each dose.

Colin_T said:

You can buy Iron (Fe) test kits and monitor iron levels in the aquarium. You want the iron level around 1mg/litre (1ppm) and no higher because higher levels affect fish and other life forms (as mentioned by Byron).

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Seachem iron is iron Gluconate It is a type of acidic sugar. bacteria consume gluconate very quickly. When the gluconate is gone the iron rusts. May people try to maintain a iron level of 1ppm with this product. Some peaple have to add iron gluconate almost daily to maintain soluble iron levels adequate for plant growth. Iron oxide is not soluble and not useable by plants. if you use a form of iron that lasts longer in the aquarium you will use a lot less

I use iron DTPA in my aquarium bacteria won't consume it and it will last a long time. Iron DTPA is used in Easy Green Fertilizer. I dose once a week to to maintain a level of 0.1ppm in the aquarium. DTPA is safe for shrimp and fish..Bacteria doesn't touch it and it is stable to about a PH of 8. Above a PH of 8 is rusts and is no longer available to plants.O.1ppm ia more than enough for good plant growth with a water change once a week with a dose after the water change.

Take a container with 100ml of distilled water and one milliliter of vinegar and 3.44 grams of iron gluconate (equvelent to 1/2TSP+1/4tsp+1/8tsp) or iron DTPA. one one milileater dose will achieve 0.1ppm of iron in a 10 gallon tank about 40 liters) after your weekly water change.

Note this recipe can be adjusted using:

Rotala Butterfly | Planted Aquarium Nutrient Dosing Calculator​

Sources of iron DTPA
https://nilocg.com/collections/fertilizer-select-salts/products/na-iron-chelate-select-salts-fe
https://greenleafaquariums.com/products/dtpa-chelated-iron-0-5lb-jar.html

Everything in moderation as pop used to say. I can tell you I never got results until I started dosing with iron. Such a small amount for a big aquarium gets lush growth. The lighting is the same as when I struggled! I only added iron- and the cheap liquid iron from Home Depot in the blue bottle gallon size.

Stan510 said:

Everything in moderation as pop used to say. I can tell you I never got results until I started dosing with iron. Such a small amount for a big aquarium gets lush growth. The lighting is the same as when I struggled! I only added iron- and the cheap liquid iron from Home Depot in the blue bottle gallon size.

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Do you do water changes?

Since the plants have filled in,I only make a small 20% or so change about every six weeks? To tell you the truth,I wonder if I should even do that?
My tap water is very soft- 0. So minerals and what have you don't build up with all the plant growth.
This is with a 4 year old established tank. The iron being the main drive.

To give you an idea how well iron works,I use about a tablespoon every other day on the 240 gallon. I would say one and a half TS at most per 250 gallons seems to be a good ratio.
The key is do it religiously every other day, or everyday half a tablespoon I suppose.

With all the talk about fertilizer and such, I just also want to mention that goldfish eat plants and I used to provide fresh “salad” (anacharis, duckweed, etc) for my goldfish to eat. If you are keeping that goldfish in that small tank, it will outgrow it fast. One goldfish needs 15-20gal minimum. I realize you may just be using that fish to cycle your newest tank though too. Your tank there appears to be on the small side for one goldfish.

For the OP? and that small aquarium? Drops every day should be more than enough in iron or fertilizers. You would be surprised how far those doses go and yet can be a big difference in quality plant growth..