Plant newbie with 6 months limited growth

[froggytank]

Hi all, what a lovely forum. All my information is below. I don't have a green thumb and I was wondering about how best to promote growth in my tank with minimal intervention. For the first 6 months, everything grew like gangbusters, with the java fern breaking the surface, the Amazon sword 8 inches wide, and the duckweed multiplying in scoops. Then over 3 months the Amazon sword got wispy and died, the java fern reduced to half height, and the duckweed stagnated and turned lighter. This has stayed stable for another 3 months. In general I'd prefer to keep costs and interventions to a minimum and not give risk to the animal inhabitants as well. Here are my questions in no particular order:

A) What is your diagnosis for the stagnating growth and what can be done about it sustainably?
B) Are the black spots on my Java fern cause for concern? (picture attached)
C) What plants could I acquire that might thrive in my environment and substrate?

The tank:
1. Size of tank: 35L Dennerle Nano Tank 40cmx32x28; heater set to 76 degrees F
2. Age of the system approximately: 1 year
3. Tap water parameters: I don't have a testing kit; water company claims 7.4pH and hardness of 4gpg
4. Filtration and Media: Dennerle Corner Filter 40L (Corner Filter - Dennerle (EN)) no additional media besides included floss and sponge
5. Lighting and duration: ~10 hours/day Dennerle Trocal LED (Trocal Power LED 5.0 - Dennerle (EN))
6. Substrate: Dennerle Borneo Brown nano gravel (which I was sure was sand until looking it up now) Dennerle Nano Shrimp Gravel - Borneo Brown-2kg
7. Co2 dosing or Non-dosing: nothing
8. Drop Checker: none
9. Fertilizers used + Ratios: none
10. Water change regime and composition: weekly ~40% with a siphon and Seachem Prime in the tap water
11. Plant list + Invitro/Emersed: java fern, pothos, duckweed, grass I can't recall, unknown arugala-like stowaway
12. Inhabitants: 3 African clawed frogs, guppy, platy, pleco
13. Full tank shot and surface image

 

[hypnogogia]

9. Fertilizers used + Ratios: none

That’s your problem. You need to feed your plants if you want them to grow, so you might want to start using an NPK fertiliser. I think in the US NilocG is a good one.

 

[froggytank]

That’s your problem. You need to feed your plants if you want them to grow, so you might want to start using an NPK fertiliser. I think in the US NilocG is a good one.

Thanks for your reply. The inhabitants don't provide enough for the plants? And a fertilizer such as that, won't it possibly cause a nitrate spike?

 

[John Troy]

Although I cant be certain, I don't think fish waste provides many micronutrients, mainly just nitrates, so it may be useful to add a micronutrient fertiliser. Given you don't have much plant mass I think it would be unwise to add more nitrates, especially since your highly stocked already. Obviously CO2 injection practically always helps plant growth. In terms of plants that would do well, given you dont have tons of algae despite low plant mass and high stocking it means your tank probably doesnt have an excess of nutrients and your light probably isnt very strong, also your substrate isnt particualy nutrient rich, so the best plants to go with would probably be something like anubis or bucephalandra which are easy to grow and you could attach to the rocks/wood in the centre. Anarchis elodea is always a good options since it grows rapidly in practically all conditions and also oxygenates your water, also it can be floating or rooted, either way it obtains nutrients through the water column. Although it may outcompete your slow growers in low nutrient conditions.

Thanks for your reply. The inhabitants don't provide enough for the plants? And a fertilizer such as that, won't it possibly cause a nitrate spike nutrients necessary for plant growth, mainly just nitrates.

 

[hypnogogia]

Fish add some, but not sufficient, otherwise your plants would be thriving. As to nitrate spike, your plants will use the nitrates, so I wouldn’t worry about it.

Also, it’s not lack of CO2 as your floating plants (which are not CO2 limited) are also not growing. They look pale and under nourished.

 

[MarcusA]

Fish food provides nitrogen, phosphorous, and many micronutrients. It’s not so good at providing potassium (K) and iron (in a usable form). Most here contend that N and P fertilizer are harmless even at high doses and that nitrates are only a concern in that they act as an indicator of organic waste in unfertilized tanks. Nonetheless, if you are looking to minimize your fertilizer intervention, try adding just potassium sulfate and ferrous iron. You can use seachems potassium and iron products if you want an off the shelf solution.

 

[Bradders]

I would also say that plants grow. More growth, more demand on food. It is possible there was enough ‘food’ (although nutrient deficient) at the start but now the fish waste can no longer support the plants size and demands.

 

[keef321]

Agree with others here, it is likely due to lack of fertiliser. We know the duckweed is getting access to co2, 10 hrs of light, but stagnating, therefore this points to a lack of food = fertiliser. We wont know exactly which food they are missing, so use a good all in one.

 

[dw1305]

Hi all,
What @keef321 says. I'll add in his tank pictures, as they may be of interest - <"Cloudy Water Hazy Water and Algae!">.

And a fertilizer such as that, won't it possibly cause a nitrate spike?

Again what the others have said. Nitrate (NO3-) levels will rise, but NO3 isn't actually toxic to fish until you get to <"very elevated levels"> & <"Nitrates">.

It is only really planted tank keepers who add nitrate (via a compound like potassium nitrate (KNO3)) and we do this because nitrate levels fall in our tanks as it is taken up by plants. In other cases the high levels of nitrate are the "smoking gun" of the microbial oxidation of ammonia (NH3) and nitrite (NO2-) and these compounds are toxic.

cheers Darrel