What are the challenges and limitations of "no fertilizer" planted tanks?

[saint_abyssal]

I've heard a lot about people setting up aquaria to function as miniature ecosystems that can function with few artificial inputs like fertilizer. This naturalistic approach to fishkeeping appeals to me a lot more than relying on expensive products, frequent maintenance, and "artificial life support" more generally. That being said, I think most aquarists with planted tanks use some kind of chemical fertilizer rather than relying solely on their water chemistry and fish waste. That makes me concerned about whether or not the "natural" approach is sustainable or so limiting as to suck the fun out of the hobby.

So, in your opinion or experience what are the challenges and limitations of trying to run a planted aquarium without using chemical fertilizers?

 

[Aiken Drum]

Give it a go and let us know how it goes.

There isnt going to be a one size fits all size answer. What works in one aquarium wont work in another. One persons tap water might be high in minerals and nutrients and provide sufficient, another might not. Aquarium plants tend to do better in harder water than softer water. Low nutrient demand plants will be more self sufficient than high nutrient demand plants and regular water changes might be sufficient to provide the nutrient needs.

Plants will always benefit from a fertiliser, because all the nutrients and minerals that plants need arent going to be present with just fish waste.

Growing aquarium plants is about a balance of nutrients, carbon/ CO2 and light. One will always be the limiting factor, and if there is too much of an excess of the other 2 factors that might lead to unhealthy growth (and algae). A friends aquarium has no aquarium light for instance, they dont dose any nutrients, but their plants are healthy. They don't grow very fast (if at all) due the lack of light and nutrients, but its healthy growth because there are no deficiencies and the plants are low demand. If they added an aquarium light, the plant would try to grow faster, but this could lead to unhealthy growth as there are insufficient nutrients to support that growth rate. If they added more demanding plants, they might find (almost certainly find) that there is insufficent light and nutrients and the plants would just die over time.

You also mention not wanting frequent maintenance. Another person i know does no water changes for instance and his plants thrive. But he does a lot of other maintenance. One thing low demand plants use is carbonate hardness (KH) because they get their carbon from KH rather than CO2. So over time the carbon gets depleted due to plant growth if its not replenished through a water change. The person mentioned above has to add alkalinity buffers to his aquarium to restore the KH. So we are swapping water changes for maintenance of another kind. He also stocks his aquarium very lightly with fish. He is probably more interested in the plants than the fish if im honest.

 

[saint_abyssal]

One persons tap water might be high in minerals and nutrients and provide sufficient, another might not. Aquarium plants tend to do better in harder water than softer water. Low nutrient demand plants will be more self sufficient than high nutrient demand plants and regular water changes might be sufficient to provide the nutrient needs.

Here is a lab print out of my water chemistry.

Plants will always benefit from a fertiliser, because all the nutrients and minerals that plants need arent going to be present with just fish waste.

What do plants need that fish don't?

You also mention not wanting frequent maintenance. Another person i know does no water changes for instance and his plants thrive. But he does a lot of other maintenance.

What kind of other maintenance does he do?

 

[Aiken Drum]

Common nutrient deficiencies in aquarium plants are iron, calcium, manganese, magnesium, potassium and carbon. An all in one fertiliser like seachem flourish contain all those in sufficient quantity for low demand plants. They also need nitrogen, phosphate and CO2/ carbon. There is commonly enough of these in aquariums from fish waste, respiration and gas exchange from the atmosphere for low nutrient demand plants. But if you are keeping high nutrient demand plants you may need to dose fertiliser with nitrogen and phosphate and inject CO2.

As for additional maintenance, he is constantly trying new things, seeing if the things he tries has a positive or negative effect, and then tweaking things further. Sucessfully growing aquarium plants can often be a process of trial and error.

There are fertiliser dosing regimes like estimate index that ensure plants are never nutrient deficient. There are monitoring processes like duckweed index that will highlight nutrient deficiency. These arent really what i would consider low maintenance though.

I have very successful planted aquariums, i just do a weekly 50 to 75% water change, and dose seachem flourish with a water change. I keep a variety of low demand plants under decent lights and i have moderately hard water. One thing thats important is that not every plant does well in every aquarium. Keep the ones that do well, get rid of the ones that dont.

Your water analysis shows potassium levels are low for a planted aquarium. You havent said if the analysis is from your tap or in the aquarium. If you see signs of potassium deficiency a fertiliser should provide that.

 

[saint_abyssal]

There is commonly enough of these in aquariums from fish waste, respiration and gas exchange from the atmosphere for low nutrient demand plants. But if you are keeping high nutrient demand plants you may need to dose fertiliser with nitrogen and phosphate and inject CO2.

I've compiled a list of plants of interest. Do you think I could keep any of the following without fertilizer dosing?

Surface floaters: Water lettuce (Pistia stratiotes) and red root floaters (Phyllanthus fluitans).

Background plants: Yellow Flame Bacopa (B. caroliniana), coontail (Ceratophyllum demersum), Elodea canadensis, and Leopard Vallisneria (V. spiralis).

Middle to back: Dark Red Ludwigia repens and red tiger lotus (Nymphaea zenkeri).

Midground: Lesser creeping rush (Juncus repens) and Pink Flamingo Cryptocoryne wendtii.

Fore-to-midground: A blue cultivar of Bucephalandra, Pink Cryptocoryne becketti petchii, and narrow-leaved arrowhead (Sagittaria subulata). Foreground: Banana lily (Nymphoides aquatica).

One thing thats important is that not every plant does well in every aquarium. Keep the ones that do well, get rid of the ones that dont.

I like this approach. What's the best way to implement it, though? Like plant a few desired species of root feeders and stems while having a large number of "easy" water column and surface feeders handling the actual nitrates and oxygenating the water until it's obvious whether or not the experimental plants are a good fit?

Your water analysis shows potassium levels are low for a planted aquarium. You havent said if the analysis is from your tap or in the aquarium. If you see signs of potassium deficiency a fertiliser should provide that.

The analysis was for my well water. I don't actually have a tank yet. I'm trying to design the aquaria to need as little maintenance, artificial inputs, and technological support as possible. I'll definitely need to add potassium to the aquarium, but I would prefer it in the form of potassium rich food instead of something I'd need to buy separately.

 

[Danio8]

I have water lettuce doing quite well in both unfertilized tanks and lightly fertilized ones. Granted, the tanks do have a fairly high stock

 

[Aiken Drum]

The water lettuce and red root floater are both going to be in areas of the tank with maximum light and access to atmospheric CO2. So the limiting factor with both of these plants will be nutrients. If these plants do well its safe to say the rest of the plants will have enough nutrients too. Thats what "duckweed index" is, its fairly safe to say the same with these floating plants too.

Of your background plants the only one i would say is low nutrient demand is the bacopa caroliniana. I would be dosing ferts for the other 2, and they would all do better with root tabs.

Your mid plants, i would expect to be dosing ferts with root tabs for all of them.

The foreground plants. The sag will probably need injected CO2. It might do ok without, but maybe not. I would be dosing ferts with root tabs. Don't know anything about the bucephalandra, but what ive read it might do ok.

Honestly, just from the amounts of different plants you are considering it sounds you are going down the heavily planted route, and that will benefit from some nutrient input, possibly injected CO2 and a soil based substrate. Its not going to be low maintenance. If i was attempting to go fertiliser free, i would only be looking at a small amount of plants like anubias and java fern and take it from there. The sort of aquarium it sounds like you are attempting is going to take a lot of work.