# Adding new substrate over existing in an established tank



## Karen00 (Sep 19, 2016)

Hello all,

I'm looking for some guidance about adding a layer of new substrate over my existing in a freshwater setup. My tank is a 15g.

The tank has been going for about 2 years and my substrate is the CaribSea Joe's Creek which is about the size of pea gravel. I want to add an inch or two of sandy type substrate for some bottom dwellers I plan to get. I plan to remove about an inch of the existing substrate to try and keep the depth of the water column about the same.

My question is... Can I add the layer all at once or will this kill the beneficial bacteria (effectively suffocating it) that lives in the substrate? I'm concerned about a crash. If a crash is a possibility then is it best to do a quarter of the tank at a time (or maybe just an eighth)? If this is the best route then approximately how long would I let each section sit to build up enough bacteria before moving on to the next section?

Thanks!


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## wtac (Mar 17, 2006)

With FW, the bulk of the biological work is done withing the filter system, substrate doesn't add significantly to the biological work.

The issues with adding a different grain size is that the smaller grains will settle to the bottom over time filling in the voids b/w the pea sized gravel.

Substrate layer without a rooting network from plants is problematic at thicker layers greater than 2". With smaller voids b/w substrate particles, you risk anaerobic decay with thicker substrate layers unless you are steadfast with weekly water changes with gravel vacuuming.

With that in mind, a mixed large grain and sandy grains will give a great look but don't have the gravel layer any thicker than 2" to minimize issues. Gravel vac well prior to removing the desired amount of pea sized gravel and then add the sandy substrate (after its rinsed).

HTH


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## Karen00 (Sep 19, 2016)

wtac said:


> With FW, the bulk of the biological work is done withing the filter system, substrate doesn't add significantly to the biological work.
> 
> The issues with adding a different grain size is that the smaller grains will settle to the bottom over time filling in the voids b/w the pea sized gravel.
> 
> ...


Thank you so much for this reply!!

I forgot to mention that my current pebble substrate is about 3" thick. I planned to remove 1" of the pebbles and would then add 1" of a sandy type substrate over the pebbles. I was looking at the CaribSea Naturals substrate because they specifically say they are safe for soft bellies which is what I need. I was looking at either the Moonlight Sand or Sunset Gold found here: https://caribsea.com/aquarium/# (you have to scroll down to Freshwater/Super Naturals). If you have any thoughts on this let me know. 

My plan is to mix my current substrate with the sand so that the sand fills in all the spaces in the substrate. Once the gaps are filled I would continue to add the sand to a depth of 1". This means the base would be sand and pebbles topped off with the sand layer. I figure if I don't fill in the spaces then my 1" layer would continue to disappear until the gaps are filled regardless.  Is this the correct approach? Does this make my base too compact?

Should I just do 2" total (1" pebbles, 1" sand) or is 2" pebbles and 1" sand fine?

I am religious about doing my weekly water changes and siphoning the gravel. I also forgot to mention this is a planted aquarium.

You mentioned about doing a gravel vac before adding the sand (thanks for bringing this up). My question regarding this is whether I should do this to try and get as much gunk out of the substrate as possible before adding the sand or is doing a gravel vacuuming more to minimize a bunch of gunk getting kicked up as I go through the process of removing pebbles and adding sand?

Thanks again! I have never attempted this and want to be sure I do it properly to avoid upsetting the water parameters and throwing my tank into a mini cycle.

Cheers.

Karen


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## wtac (Mar 17, 2006)

The sand will be fine to add and it doesn't really matter how you add it in the process AS LONG AS you do a good gravel vac to suck out as much of the accumulated detritus to minimize trapped crap that may cause problems. 

A planted system with more than 50% of the substrate that will have a rooting network, I don't think you will have much of an issue down the road but it's all about preventing/minimizing/foreseeing issues.

If it's about adding sand in the open areas, just address that area...no need to do the whole thing . You will notice over time, 6mo-1yr, that the sand layer in that area will "disappear" as its will be settling in the pea gravel area where the plants are.

HTH


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## Karen00 (Sep 19, 2016)

wtac said:


> The sand will be fine to add and it doesn't really matter how you add it in the process AS LONG AS you do a good gravel vac to suck out as much of the accumulated detritus to minimize trapped crap that may cause problems.
> 
> A planted system with more than 50% of the substrate that will have a rooting network, I don't think you will have much of an issue down the road but it's all about preventing/minimizing/foreseeing issues.
> 
> ...


Thanks again for your advice!! Now I just have to set about doing it. Getting the new substrate in won't be too much of a hassle but getting the debris cleaned from the bottom of the existing gravel is going to be a pain. I wish I thought to do a mixed substrate from the start.


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