Plants aren’t growing in fishless tank?

[JackGulley]

So as y’all know I’m setting up a second tank. I got the tank, substrate, sponge filter, and water (dechlorinated) set up about 3 weeks ago, but refrained from adding anything else just yet because I had to be away from home the past two weeks. My plan was to insta-cycle the tank once I had fish by squeezing out the filter sponge from my other tank.

So now comes the topic at hand. I know I want floating plants in this tank, AND that they are desirable for the fish I plan to add first (pencils). My community tank had a small amount of red root floaters in it, but the population never got above a handful of plants because they would get knocked around by the HOB filter. So I decided to just transfer the remaining red roots to the new tank, and hopefully they would cover the surface in the three weeks I couldn’t do anything else. However, instead proliferating rapidly like I expected them to in a tank with lower flow, they all melted and did worse than in the other tank. At first I thought the problem might be that there weren’t any nutrients in the fish less water. So before I left, I added a few pieces of fish food to decompose and went ahead and squeezed the dirty filter sponge in there. But when I came back after two weeks, the plants were in the same condition! There are about two plants alive at a given time, and those melting, and a lot of dead plants on the bottom.

The tank water is dechlorinated, the filter is in place, and I’ve got a desk lamp for light, although I haven’t added a heater or an actual aquarium light yet. What’s going on? Do I need to add ferts?

 

[Seisage]

I have learned that floating plants are more difficult to keep alive and healthy than they're made out to be. My amazon frogbit started out happy and healthy and has slowly dwindled and withered over time. I'm not sure of the cause, but my suspicion is a lack of nutrients. They really do use a lot. A few fish flakes and a filter squeeze aren't going to be enough. If you can salvage the remaining plants, I'd definitely look into fertilizer.

Also, just as a note, the "insta-cycle" you mentioned won't truly be achieved by just squeezing out old filter media. More likely, it'll just foul your water. The nitrifying bacteria live on surfaces, and sort of "stick" to them. It's why you can squeeze sponge media to hell and back while cleaning it and still have a functional biofilter. It's true you might get some bacteria out with a squeeze or two, but likely not enough for an instant cycle. If you have the ability, I would instead recommend taking some old sponge media and actually placing it in the new tank. Leave it there for about 3 weeks and that should be enough to colonize your new filter.

 

[JackGulley]

I should’ve clarified that I also left a piece of sponge from the old filter in the tank.

 

[Fishfunn]

The next fish in cycle aquarium I will start, I am going to incorporate the Nitra-Zorb to protect the fish and safely start up the nitrogen cycle. The manufacturer's studies show that using Nitra-Zorb did not impact the biological filter's development. Nitra-Zorb's Efficacy Removing Ammonia, Nitrite in New Aquarium

I have used this product before and had good results. Its for setting up an aquarium and temporarily protecting fish from elevated ammonia, nitrite, and nitrate levels in the tank.

 

[GaryE]

The first thing that strikes me is "desk lamp". I've used them. Some plants grow, but most don't get the light spectrum they need.

I get wordy, so you can skip this, BUT you are trying the leftovers from an old idea. Magic water was a 60s 70s part of the balanced aquarium myth. They didn't understand the bacteria and archaea cycle yet, and thought aged filthy water had transferable properties to do what we have learned the cycle does. Squeezing filter waste and using old water were established techniques that did... nothing. Some people thought they worked, and said so, and like all bad ideas, they linger on in fish lore.

What we didn't get back then was that cycled tanks tended to have older water in them, because they were older tanks. The bacteria and archaea are on surfaces, working away to feed themselves.

I've seen it advised so many times, but its usefulness is limited. It's just water that should have gone into the houseplants.

Putting an old piece of sponge in is like dropping a lung on the floor. The cycle is dynamic. In a filter, with flow bringing it food and oxygen, the surfaces of that sponge could have come to life. I see every aquarium as a living creature, alive through its bacteria and archaea populations (much like us, disturbingly).

There's no substitute for cycling. It doesn't have to be the ammonia/fishless type. You can run your filter on the established tank for 3-4 weeks, and just switch it over. I put a seeded filter like that into a tank with some plants from an established set up and can add a pair of small fish to a 10 gallon right away. But the filter has been cultivated. How? I always run a few extra filters in tanks, since as a fish breeder I sometimes have to set up quickly for surprises or quick developments.

 

[Colin_T]

How long is the light on for each day?
Is the light globe fluorescent or LED?
How many watts is the light?
What is the Kelvin (K) rating of the globe?

What are the tank dimensions (length x width x height)?

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It's usually a lack of light or lack of nutrients. Plants need at least 8 hours of light per day and can have up to 16 hours of light per day. However, they need 8 hours of darkness to rest so depending on how long the light is on for, you might want to increase the length of time it's on.

Most plants do best with some nutrients and an aquarium plant fertiliser might help. If there's no fish in the tank then get a complete fertiliser that contains nitrogen, phosphorus and potassium (NPK) as well as the other micro nutrients plants need.

 

[JackGulley]

It’s a 20 long. I don’t know the specs of the light because it’s just a desk lamp I’ve had forever. It’s an LED light. I try to keep it on about 8 hours a day. My room light is also on all day so the plants are rarely actually in the dark.

The lamp and the sad remnants of my floating plants

 

[Fishfunn]

It’s a 20 long. I don’t know the specs of the light because it’s just a desk lamp I’ve had forever. It’s an LED light. I try to keep it on about 8 hours a day. My room light is also on all day so the plants are rarely actually in the dark.
The lamp and the sad remnants of my floating plants

When I upgraded to RO/DI water, my plants did very well. Are you using RO mixed water?

 

[JackGulley]

When I upgraded to RO/DI water, my plants did very well. Are you using RO mixed water?

Outside the scope of the issue right now lol. My plants do fine in my established tank, just trying to get them to grow in this brand-new tank with no fish, no heater, and no light yet. My water is also very soft already so I don’t know that will ever need R/O.

 

[Colin_T]

Room lights don't do anything to help plants in aquariums.

Move the light bar closer to the tank and have the light on for 14 hours a day. See if it helps. Otherwise you will need to add another light. You can buy LED spotlights from hardware stores and some have a clamp you can use to hold them onto things. They are pretty cheap and usually come with a globe that has a 6500K rating, which is ideal for plants.

 

[JackGulley]

Yeah, I was always intending to get a real light. I was just hoping I get get a head start with plants since the tank was gonna be sitting for two weeks.

 

[JackGulley]

I transferred the remaining plants back to my other tank and they promptly died anyway

I was planning to get different species of floaters for this tank anyway, it just would’ve been a plus if I could get those to grow