# Advice please 🙂



## mario (22 Oct 2021)

Hello everyone, I am planning my return to the hobby after a long break. I want to start from where I left, that is with a low(ish) tech tank (no CO2 injection)
As a substrate I was thinking garden centre topsoil capped with play sand. Being the sand very fine can it be an obstacle to the roots? Also does the topsoil have enough organic matter (compared to compost) to produce CO2 once decomposition is established?
I am thinking DSM to establish the roots of some carpeting plants (mini haigrass, helantium green, marsilea hirsuta), then flood, plant some stems, and use liquid carbon to help the transition to the submerged low CO2 environment. Is it worth trying or is bound to failure?
Third and last question: if we believe that exchanges between water and the atmosphere are beneficial not only for oxygenation but also to keep CO2 levels stable, would a powerhead with Venturi be useful? I will be already using a hang on back filter.
Thank you!

Mario


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## ScareCrow (25 Oct 2021)

Hi Mario, you can use topsoil topped with play sand. The sand won't cause problems for the roots. Have a look at the soil substrate thread, it should have the answers you want.
As for the Venturi question, the size of the bubbles created by the Venturi will be too big for any significant CO²/O² exchange. Decent surface agitation should be sufficient. Venturis tend to be noisy but if you like the look, go for it.


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## PARAGUAY (25 Oct 2021)

Just experiment Mario  Plants can grow in inert substrates but you need your water dosing right


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## azawaza (28 Oct 2021)

PARAGUAY said:


> Just experiment Mario  Plants can grow in inert substrates but you need your water dosing right


and if they don’t grow as fast, due to them being heavy root feeders, then just 
add to your substrate some root tabs


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## dw1305 (28 Oct 2021)

Hi all,


mario said:


> Also does the topsoil have enough organic matter (compared to compost) to produce CO2 once decomposition is established?


I'm a great <"Diana Walstad fan">, but I'd rather rely on water turn-over for gas exchange (<"both CO2 and oxygen">), rather than <"not having any water circulation"> and having dissolved CO2 from decomposition build up.


mario said:


> Third and last question: if we believe that exchanges between water and the atmosphere are beneficial not only for oxygenation but also to keep CO2 levels stable, would a powerhead with Venturi be useful?


I'm a <"venturi fan">, in fact I'm <"an oxygen fan"> generally.  Picture from <"The dissolved gas bubble.......">.







ScareCrow said:


> As for the Venturi question, the size of the bubbles created by the Venturi will be too big for any significant CO²/O² exchange. Decent surface agitation should be sufficient.


You can "cheat" by aiming the venturi at a sponge, the waffled surface sponges and PPI10 or PPI20 sponges are <"particularly good for retaining bubbles">.





cheers Darrel


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## mario (28 Oct 2021)

Thank you all very much


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## erwin123 (9 Nov 2021)

mario said:


> Third and last question: if we believe that exchanges between water and the atmosphere are beneficial not only for oxygenation but also to keep CO2 levels stable, would a powerhead with Venturi be useful? I will be already using a hang on back filter.
> Thank you!
> 
> Mario



normally we try to adjust the hang on back filter outflow to be almost flush with the water level to minimise 'splashing' as the water cascades out of the HOB .  If you allow the water to 'fall' a little distance back into the tank, the 'splashing will introduce air bubbles into the tank., as long as you don't mind the splashing noise.


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## MichaelJ (9 Nov 2021)

erwin123 said:


> the splashing noise


I have two HOBs on each of my tanks... It's more like a tinkle at my end


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## mario (10 Nov 2021)

Thanks everyone for the contributions! I am definitely going to run a 'splashy' filter and a venturi when I'll finally get to set up my aquarium. I am tempted to try a little experiment to measure CO2 with and without water agitation. I have soft water so even a small change in CO2 should be detectable with the change in pH


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## dw1305 (10 Nov 2021)

Hi all, 


mario said:


> I am tempted to try a little experiment to measure CO2 with and without water agitation. I have soft water so even a small change in CO2 should be detectable with the change in pH


Have a look at <"this post"> from @BigTom. 

cheers Darrel


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## mario (10 Nov 2021)

Super interesting stuff, thank you Darrell!


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