Opinion: Deep Sand Beds Are A No-No

[lisneydand]

Hi everyone,

New here and to this hobby. In setting up my first tank, I made a mistake that I figure is worth sharing, hence this post.

I live on the coast near a beach that has very fine sand. In setting up my tank, I simply just went to the beach and got:

1. A jug of saltwater (mixed with distilled water to the correct salinity)

2. A ziplock of sand

from the area of the beach where the waves wash up and down (the swash zone). I let the tank cycle for a couple weeks then added snails, then waited a couple more weeks before adding shrimp. I *thought* I had all my bases covered in regards to concerns (listed below):

1. Polluted water (the part of the beach I took the water from is rated as having good water quality)

2. Things in the water and sand potentially dying when they went from high oxygen / high salinity to stagnant brackish conditions (I figured it would just be taken care of during the cycle)

Everything seemed good, parameters evened out, algae grew, etc. But here is where the big mistake happened:

The night before my shrimp came in the mail, I decided to to some cleanup of the tank. I had put some macroalgae in the tank (Ulva intestinalis) and realized that it could cause problems later on, so I wanted to siphon it out. It was everywhere in these little pieces, so I essentially stirred the water to kick it (the macroalgae) up into the water column for easier cleanup. In doing this, I also disturbed the top layer of sand. About eight hours later, I tested the ammonia and it had spiked to 2 ppm... the same day my shrimp were coming in the mail... I did a huge water change and have been monitoring the parameters, with a jug of water (distilled water made brackish with reef salt) standing by. The ammonia has stayed at zero so far. I'm testing it daily.

The sand bed is about 2 inches deep and very fine grained. My inference is that one of two things happened (or both):

1. There was a bunch of microscopic dead stuff trapped in the sand, but sealed off from the water column.

2. There were pockets of anaerobic bacteria in the sand, which can release hydrogen sulfide and kill stuff when agitated.

I did some research on the subject and found that, especially with very fine grained sand, people generally recommend only using a thin layer in their tanks (a quarter inch or less).

I'm considering setting up a second tank, cycling it, and moving my shrimp into it temporarily so I can reduce the sand bed in the main tank (and let it cycle again). Otherwise, I think I just need to be careful about agitating the sand in the tank as it currently stands.

Anyways, I just had my morning coffee and figured this post might be helpful to share.

In my opinion: make sure to keep your sand beds pretty shallow, especially with fine-grained sand. I now realize why the set-up guide on here says "We also recommend adding a substrate (usually sand) to the tank, to a depth of about ½ inch." I figured that meant 'at least a half inch, or more.' NOPE.

Thanks for reading!

Edit: I realize that there could also be issues with the plankton in the ocean water dying off, but it seems too weird that the spike happened after over a month of the tank being set-up, right after I agitated the sand. That said, it probably would be better to just mix up my own water going forward. No need to introduce the potential for complications.

Edit 2: here is a video of the tank: https://streamable.com/q0w6e . Ignore the jingling (we have two kittens). There are still a couple pieces of the macroalgae in there. I plan to get it all out soon. The chunkier stuff on top of the sand is coral and sea shells. With the substrate and decorations, it holds about a gallon of water. There's a plastic cap on the top with a hole cut out of the middle; it has ridges on the underside that I figured would help discourage the snails from wandering off.

[mike.d]

A sand bed of 2 inches in the flask in the video does seem a bit deep. I wonder if another factor could be substrate to water ratio. 2 inches of sand would probably be fine in a 10 gallon tank. Even if there was a pocket of something that got released, the concentration would be less drastic in the larger amount of water.

If you collect anything from nature, it's a good idea to boil it for a minute or two before it goes into your tank.

The typical ratios are 1-2 pounds of substrate per 1 gallon of water. I try to keep it closer to 1:1 and haven't had issues.

I used to have a 10 gallon planted tank with freshwater shrimp. For that I put down an inch of potting soil then 5 pounds of gravel. This isn't really analogous to sand because the roots of the plants should have prevented pockets of chemicals from forming. I had that tank set up for a good 3+ years and nothing bad ever happened.

[Mustafa]

Thanks for sharing! I think the main problem in your case wasn't the depth of the sand substrate but the fact that you didn't wash it. With all the organic stuff in it of course there will be lots of decomposition which produces ammonia no matter how deep the layer of sand is.

[Cakelake]

My sand is about 2 inches deep and I’ve had no problems, not even when I moved my tank. No deaths and my shrimp and snails are breeding. I think as long as the sand is kept still it can be deep, although I would make it more shallow if I made another tank considering all the negative things I’ve heard about the deep sand