Potting soil under sand?

CuriousFins

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So I'm considering using Fish For Thought's idea and putting organic potting soil under sand in my planted aquarium. Just double checking, is this a good idea?

Will it help with growing a carpet of dwarf sag?

And is there anything I should avoid or look for in types of soil?
 

Byron

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Just double checking, is this a good idea?

In my view, absolutely not--at least, not if you want to have fish. A plant-only tank is a very different "kettle of fish." Obviously it can be done, but there are significant detriments to deal with, and the bottom line is, it is not necessary, nor does it really offer much benefit, if any frankly.

Will it help with growing a carpet of dwarf sag?

Not really, because this plant can be grown in play sand with substrate or liquid fertilizer just the same...I've done it with pygmy chain swords for years.
 
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NannaLou

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I tried this and it was a total disaster! Whatever was in the potting compost caused a huge algae problem and then gases built up (due to the depth I think) and I had huge, toxic gas explosions 😢. I had to strip the whole tank back to bare glass and start again. That said, it is frequently mentioned, so perhaps I missed a vital part of the preparation..?
 

xxBarneyxx

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It can work, its been done successfully many times and I have done it myself.

However in my experience its a mess and more faff than its worth. Using an "active" substrate is a valid way of doing things and my preferred method. In my experience I find it better to use dedicated "aquasoil" though. This is less messy and "safer" in that you know what's in it.

If you are using under a sand substrate you might want to consider putting it into mesh bags first. This helps keep it in place and stops it mixing with the sand.

Also two things to remember with almost all types of active substrate. Most of them will leech a lot of nutrients into the water at the start, mostly ammonia. This is generally not that big of a deal if you are cycling the tank but is something to be aware of if adding to an existing tank.

Active substrates are also not a bottomless pit of nutrients. Eventually they will run out. However depending on the type of substrate, what plants you have and a bunch of other conditions this will often take a very long time to happen. Even when it eventually does water column dosing and root tabs can be used to take over the job. I have had tanks running for multiple years using aquasoil and light water column dosing with no issues.

You will get better growth with an active substrate then with nothing. However an active substrate is not the only way to do it. Water column ferts or root tabs with an inert substrate will work also.

You also have the option of doing both. I use active substrates and light water column dosing. The active substrate means that heavy root feeders are taken care of and that I don't have to be to regular with my water column dosing. The water coloumn dosing helps out the plants that are more heavily taking nutrients from the water and also help prolong the life of the active substrate. I make my own ferts as well so I can customise to what my plants might need or what might be lacking in my source water.
 

Colin_T

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One way of looking at plant substrates is they are like potting mix in a garden pot. They might have a few nutrients in them to begin with but over time the potting mix runs out of nutrients and then you have to start adding fertiliser to the pots.

The same thing happens with plant substrates in aquariums. They release nutrients for a bit and then eventually run out. After that you have to add fertiliser to keep the plants growing fast.

If you just have a normal substrate (sand or gravel), and add aquarium plant fertiliser to the tank, the plants will still grow but you won't have mud in the bottom of the tank.
 

xxBarneyxx

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The same thing happens with plant substrates in aquariums. They release nutrients for a bit and then eventually run out. After that you have to add fertiliser to keep the plants growing fast.
This is true. Though in reality it can often takes many years for this to be a factor. In that time you get great plant growth with very little extra work involved. I've had aquasoil based tanks running with high light/CO2 and good growth for 4+ years while only dosing Micros and potassium, so it is an "issue" that for most people they will never see. Several years of good plant growth and not having to worry about nutrient issues in your plants or having to manually dose seems worth it to me. Everyone has different ideas of what they enjoy though.

I will never claim that it is necessary but it does have some very good advantages and I always try and balance the bias of this forum as much as I can when it comes to planted tanks. I don't disagree with the views, they work and I have done it that way myself. I just like to try and put out that its not the only way to do it.
 

robmcd

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Okie dokie, thanks everyone! Think I'll just stick with sand then. 🙂
Sand isn't the greatest substrate if you are going goal is carpeting plants. I personally use an inert substrate with root tabs and my monte carlo ground cover is almost out of control.
 

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