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Oyster shells, clam shells, snail shells?

6399 Views 7 Replies 6 Participants Last post by  ReefkprZ
I am trying to make a good mix for under the gravel and am wondering if there would be any benefit to adding gound shells to the mix? So far ive got mineralized wormstrate, peat, clay, and osmocote. These are all free unlimited resources for me ( minus the $5 in osmocote)and the shells are included. If theres no potential benefit then I wont add it. I just wanted to ask before it hits the tank bottom. Thanks in advance for your experience or insight! :icon_bigg
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Anyone? Surely someone has considered this idea before.
The addition of the shells might cause your pH to slowly drift upwards, as the calcium carbonate slowly dissolves. Of course, it depends on what you plan to do with the aquarium.
I use whole oyster shells in with my kreb tank, never tried them ground up. Don't notice a ph climb, but I do a weekly w/c
If your water is very soft, very low mineral content (under about 3 German degrees of hardness), then the shells will probably help.

If the tank is for hard water fish, and you want the water to be hard, then add these to the filter as well as to the substrate, and use them ground up into sand size particles. I use knee hi stockings to hold oyster shell grit and coral sand in the filters where I want the harder water.

If your tap water has a GH and KH in the range you want, and at least 3 German degrees of hardness, then I would not bother adding oystershells or other sources of minerals. The plants will do fine with GH and KH of 3 or more.

Once you get this set up, test the water before doing a water change. If the GH and KH is much harder in the tank than in the tap water then you should do small water changes, or prepare the new water with mineral additives so it matches the tank. Then larger water changes are OK.
Diana, you are a good person to ask this question to. I dont want to adjust my Ph, Gh, or Kh. I was considering if the plants might be able to use some of the nutrients slowly released to their roots. Most notably Ca, but any other minerals in them as well. Kind of a mix between a Walstad tank and a mineralized top soil tank to try to reduce the need for EI dosing. Or are you guys already telling me theres no benefit other than adjusting ph etc...?
I think the amount of minerals in snails shells will be inconsequential considering the amount of minerals in your MTS. If you add them to the substrate, there won't be a lot of flow through there to shake up your water column, but I really doubt your plants with benefit any from them. Like I said, the MTS will have more than enough minerals.
the calcium carbonate found in the shells will slowly dissolve into your water column, a suprisingly high PH. 7.0 is low enough to dissolve calcium carbonate into your watercolumn. which is funny since 7.0 is considered neutral. if you inject co2, further lowering your ph, the shells/pieces will slowly dissolve releasing both calcium carbonate as well as the byproduct of carbon dioxide. Water with a pH maintained to 7 can dissolve up to 15.9 g/L of CaCO3.

this is one reason Co2 reactors with crushed coral are used on marine tanks, to keep calcium levels high, any calcium carbonate based media works but crushed coral is more easily dissolved than oyster shells, but the fact remains that between the low ph of the tank water, and the organic amino acids released from the break down of your mineralized topsoil as well as the detritus break down from fish waste the shells will slowly be dissolved of all calcium carbonate, which will constantly be pushing your PH upwards slowly increasing, the amount of CA2+ in your water. I'm not sure what the final equil;ibrium will be having never attempted this in a mixed bed tank, but the chances are your stable ph level could be slightly higher than with MTS alone, at least untill all the available CaCO3 is dissolved.

also a warning with the freely available dissolved ca if you dose any bicarbonate or calcium you run the risk of calcium precipitating out of solution. but I doubt that you will have levels high enough to worry about that in a freshwater tank, just figured I would mention it.
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