Plants not growing in pool filter sand?

Hi all. I have a 20 long that I've had setup for about 3-4 months.
I'm using pool filter sand as the substrate and have only crypts.
I mostly have Crypt Balansae, but also some wendtii too. That said,
I used to have a previous set up that was quite similar but it was in a 33 long.
Same lighting, basic setup, except for I was using caribsea sunset gold sand.
My plants, which were mostly crypts and rotala, used to grow like weeds.
However, my plants basically aren't growing it seems. I don't know if it's because
the pool filter sand isn't quite as fine as the caribsea, or what. But, regardless, I'm not seeing
any kind of noticeable growth.

I'm thinking about just swapping out to the caribsea sand again. Not a fan of the cost, but I can usually get it on sale.
I've used it multiple times, and each time I've had success with plant growth. I do only low-tech, but still love
the growth I used to get. Several plant species would basically have to be trimmed basically every couple weeks.
I also don't do fertilizers. Never have. Even in my previous tank, the only form of fertilizers were fish waste.
I've also always used the same lighting, a standard, original Finnex stingray fixture. Only difference being the size
of the fixture, as in my 20 long, it's 30 inches long and my old 33 long, it was 48 inches long.

Any thoughts?

What is your gh/kh. I've found that most of the commonly available crypts will do better in harder water - they can grow in soft water but it takes a 8 to 12 months for them to adjust. While this depends a lot on the time and specific species - Balansae seems to do better in soft water and red/brown wenditti - green wenditti will really struggle.

I use mostly pool filter sand and with the right plants can grow plants like these two aquariums:

Both have pool filter sand (hth brand) and extremely soft water kh and gh below 1.

If you have harder water those plants should take off after 3 or so months.

I'm not entirely sure honestly. I'd have to look into it. All I know is that in my past experiences, Balansae honestly took off pretty quickly.

I've had my old 33 long setup more than once, in various different places. Had it setup at one location, and they grew crazily. We moved and I setup the tank again with the exact same things, i.e. substrate, filtration, and lighting, and they also grew like crazy. I moved across counties, which might have had varying degrees in water qualities, and they still grew.

I'm perplexed by this. I'm wondering it could be the possibility that I have a smaller tank, so fewer fish, so less fish waste to act as fertilizer.

. . . I'm wondering it could be the possibility that I have a smaller tank, so fewer fish, so less fish waste to act as fertilizer.

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That's possible, and also tinylostwine made a good point about gh and kh. Crypts do very well in pool filter sand, quickly spreading so that they need to be thinned, in pool filter sand with my hard water.

Ugh. This makes me miss my old 33 long.
Unfortunately, I do not have the space for such a big/long tank anymore. The biggest I could probably accommodate is something that is 36 inches long and I'm not really personally a fan of 40 breeder tanks.

Crypt balansae growing in 1-gallon vases with pool filter sand: the one on the left receives GH/KH minerals, while the one on the right is kept in pure water: Cryptocoryne balansae | Aquarium Plants Forum

I’m also very much in favor of using fish waste as the nutritional foundation. That said, I ran into a similar situation where nothing seemed to grow for quite a while. I added a Tenso mix of chelated trace elements, and that seemed to kick-start growth. I can't tell for sure obviously, but traces from waste can remain bound in solids for a long time rather than becoming soluble ions. Also, it is not uncommon in aquaponics (fish-plant systems) to supplement with traces.

I suspect your move changed your water and now you have to adjust to that change.

Just so you know, the only difference between pool filter sand and Carib Sea Gold is what you’ve noticed.

The Carib Sea has much smaller particles, as it is an exceptionally fine sand but is composed of silica just as the filter sand is.

I wouldn’t expect a slight difference in texture alone to have much if any effect on aquatic plant growth.

Transplants rather frequently do something that terrestrial gardeners call sulking, which is to say transplant shock, after transplanting.

Crypts are infamous for completely melting away, but you didn’t mention that.

I would suspect transplant shock as a cause for them not having grown as yet.

They are probably devoting their resources to reestablishing roots, which is definitely doing something, but we can’t see it happening so it looks like they’re doing nothing.

I would advise being patient for another couple of months at least before doing anything drastic and that would definitely include changing the substrate.

If you’re very impatient, you might consider rooting a few willow twigs in the tank. Rooting willow produces a lot of auxins, plant hormones that stimulate root development. It isn’t safe at all to use commercially produced rooting hormones in a tank because a lot of them have additional ingredients that can be very harmful to aquatic life, such as antifungal chemicals.

But using willow twigs to supply naturally occurring auxins isn’t dangerous.

Additional auxins might help the plants establish their roots more quickly but they won’t cause a problem whether they do or not.

I suspect your move changed your water and now you have to adjust to that change.

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I moved six years ago.

Just so you know, the only difference between pool filter sand and Carib Sea Gold is what you’ve noticed.

The Carib Sea has much smaller particles, as it is an exceptionally fine sand but is composed of silica just as the filter sand is.

I wouldn’t expect a slight difference in texture alone to have much if any effect on aquatic plant growth.

Transplants rather frequently do something that terrestrial gardeners call sulking, which is to say transplant shock, after transplanting.

Crypts are infamous for completely melting away, but you didn’t mention that.

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Yeah, like I said.. I moved six years ago. This isn't anything recent. I had my old tank setup for about 6-7 months at my old location in 2020, and then I moved to my current one and had the tank setup for years the same way. Same substrate, lighting and all that. Plants grew exactly the same as when I had tank setup at my previous location.

I finally tore this tank (33 long) down in March of 2025 and then sold it. I setup this new tank (20 long) I posted about in April.
Yeah, I dunno. I might switch to Caribsea again just to see if this has a significant impact on plant growth at all.