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TDS Rise in new tank

Nick potts

Nick potts

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Joined
25 Sep 2014
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Torbay
Hi all.

Setting up a new tank for some crystal shrimp, I have used lava rock for the scape and tetra soil for the substrate (the tetra stuff is just a hard clay), Pure RO/DI to fill it and daily 100% water changes and I am still seeing a large rise in TDS and GH.

TDS went from 0 to 300+ and GH 0 to 12. Any idea what might be causing this? I chose the hardscape etc as it is inert and not supposed to affect parameters.

TIA
 
Hi @Nick potts

My understanding is that lava rock contains alkaline oxides of potassium and sodium. So, not only would I expect lava rock to increase GH but also KH and, consequently, pH. Do you have any measurements for GH, KH and pH?

JPC
 
Hi Jay.

GH was around 12, PH 6 and don't know the KH.

I have used lava rocks in other tanks and have never experience a TDS rise like this before (it is always sold as inert). I may have to test some of the substrates
 
Substrate I agree but I have never had this problem before with lava rock. I will have to test bock rock and substrate with some fresh RO/DI.

To give you an idea of what i am up against it has gone up 50PPm in the last 30 mins
 
It's tetra active substrate.

From what i can tell it is just baked clay and is not active (it doesn't lower PH)
 
Nick potts said:
It's tetra active substrate.
Click to expand...
I can't comment on the ph effects (trying to get a accurate & stable reading in low Tds water is difficult with my ph pen) but I can shed some light on how Tetra active impacts Tds.

Slightly Heath Robinson - esque test.

So assuming this is the same product.
20220626_045423.jpg


I put 100ml of it in to 1L jug and washed it until the water was clear. Here you can see Tds reading of straight tap water.
20220626_052448.jpg


Next up reading of substrate in jug immediately after washing (800ml of water added. 8-1 water/substrate ratio.)
20220626_050156.jpg


20 minutes later.
20220626_052237.jpg


And finally after 1hr.
20220626_055726.jpg


So not much change in an hour, however, if I then give the jug a good old stir this is what we get.
20220626_055957.jpg


2x 90% water changes and we're back to low Tds, will leave substrate in jug for a few hours, stir and take final pic.
20220626_072820.jpg



Not sure this would account for a 300 ppm rise in Tds but it does show Tetra active when new will leach something into the water column, especially if it gets disturbed. I suspect after a few water changes this Tds rise will diminish. To be continued...

EDIT.
Stirred the jug with the new water in it at 30 mins and again at 80 mins, the evidence from this simple test suggests whatever leaches in to the water column is relatively short lived.
Probably best you try the same experiment Nick, just incase your substrate contains a different mix to mine.
20220626_084727.jpg


Cheers.
 
Last edited:
@John q thank you so much for taking the time to run this test.

This is exactly what i did last night and your results are pretty much exactly what I got. Started off with 0TDS water and half filled the jug with the substrate, this gave a small rise in TDS, left it and it didn't change much over the next 30 mins or so, but stirring it did bring TDS up, this morning it was sitting at 160ppm and a stir brings that up to 220ppm.

Not really sure what to do, can't really be bothered to pull the tank apart, but sudden increases in TDS won't work for this setup.

Also, have a huge piece of the lava rock that was soaking overnight and that went from 0 TDS to 10, but that was in an open container in a kitchen so stuff would have likely got in.
 
Nick potts said:
Not really sure what to do
Click to expand...
I would have thought a good few water changes will lesson the Tds rise, is it possible to disturb the substrate at all and then do a couple of big water changes?

I have about 6L of this in a 240L tank and I've never really noticed any major increase in tds after adding it. Only thing I do is soak it for a day or so before adding it, maybe this removes any residual chemicals.

Nick potts said:
thank you so much for taking the time to run this test.
Click to expand...
No worries mate, I was awake at 4.30am and bored 😆
 
John q said:
I would have thought a good few water changes will lesson the Tds rise, is it possible to disturb the substrate at all and then do a couple of big water changes?

I have about 6L of this in a 240L tank and I've never really noticed any major increase in tds after adding it. Only thing I do is soak it for a day or so before adding it, maybe this removes any residual chemicals.


No worries mate, I was awake at 4.30am and bored 😆
Click to expand...
Yeah I can mix the substrate a bit, there is no livestock in there but lots of rock, I have 7ish ltrs in the tank (40ltrs ), I will be doing another 100% WC this eve so will report back.

_Maq_ said:
Do you inject any CO2?
Click to expand...

I am injecting CO2
 
Nick potts said:
I am injecting CO2
Click to expand...
I've got no personal experience with Tetra Soil. I assume that it's not fully burnt (like a brick) but only half-burnt clay (400 °C or so). So its CEC is preserved. Since you make the water acidic, you replace Ca2+ ions on exchangeable sites by H+. That's why TDS increase is more remarkable than in tap water.
 
I can test that as well, I'll stick a diffuser in the jug and let you know :)

Probably over thinking it and it will slowly stop going up as @John q says, but as it's crystal shrimp I would like it to be as stable as possible, so if it was CO2 I could turn that off as there isn't anything in the tank that really needs it.
 
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