Used substrate? Tank transfer Q’s


MFK Member
Nov 7, 2018
Our new 120 tank came with substrate he had fish in until 2days ago. We were going to re-use it, thinking it probably has good bacteria in it but the longer it sits in starting to wonder if it’s ok to use?

we have 2 fish, a single 4“ goldfish and a 14”pleco. We want to add a few fish. If you’ve seen my other posts you know our Goldie has been having a hard time (current 37gal) with oxygen levels.

Also wondering about:
-Using a mix of sand with the gravel, either mingled or as a layer above the gravel

-read silica sand (any limestone related) can increase ph, what about using montmorillonite clay based sand like Turface? Does it need to be changed out/have additional upkeep?

-investing in a dissolved oxygen meter or ppm test kit (and what is a ‘good’ level for either)

-how many/what type of fish we can add safely

thanks! Any other thoughts on the tr



Silver Tier VIP
MFK Member
Mar 26, 2008
Medina, Ohio
Mixing sand and gravel usually results in the sand being on the bottom. I've never used used substrate from another fish keeper but would recommend cleaning it and possibly disinfecting it if you don't know the person or if there was any chance they had disease in their tank.

I don't see any reason to invest in a DOX meter, usually good surface agitation of the water provides enough O2 in the tank.

I can't advise on other fish to add. Goldfish don't require a heater in the tank so you will have to choose what fish you will be keeping.