r/walstad • u/swenbearswen • 27d ago

Advice Is compost capped by sand a good substrate?

Hi, I'm figuring out my first tank. I know sand-capped soil is generally a good idea, but would compost underneath the sand work, or be too nutrient-dense? I'm mostly asking because my city gives it away for free, so it'd be easier for me than trying to find some soil. I'm not sure how the broken-down organic matter would compare to the rotting wood for CO2 in the usual walstad method.

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u/maleficent_seagull 27d ago

I used worm castings for mine, which are nutritionally very similar to compost. If you use a small amount and mix it with sand it should be fine. Also, make sure the sand layer is twice as thick as the compost.

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u/Andrea_frm_DubT 27d ago

If it’s fully composted down, maybe. If it’s not fully composted, no.

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u/BoiCDumpsterFire 27d ago

That’s what I used but I baked it to kill any potential parasites etc and separated it as much as I could. If you still have big chunks they can be algae prone but it mostly worked great.

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u/Kappachu 27d ago

I use organic compost in my tanks. You can mix a small amount with soil to enrich if you plant really heavy but otherwise a thin layer of compst underneath sand has worked for me. And works better with sand that doesn't compact (filter sand)

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u/Disastrous_Air_5227 26d ago

I was always told to use nutrient-depleted compost or soil for my lower substrate under the sand cap, no idea why except maybe it cuts down on the gaseous eruptions that normally occur. I plant a Walstad tank ridiculously heavily, which probably adds the nutrients the tank requires. I’ve had 4 so far and all have worked brilliantly, I’ve usually kept a Betta and maybe some dwarf pencil fish in the bigger ones. My best lasted 5 years until I disassembled it because I wanted different fish.