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CO2 in Brackish Planted Tank?

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I am setting up a new brackish tank for a figure 8 puffer, and plan on trying some plants. I plan to try a few of the faster growing plants first to see how they do and will acclimate them from freshwater to brackish over at least a week or two if not more. I love planted tanks, and while I know it is challenging in brackish I am up for the challenge.

So here is my question. Does anyone have any experience with using CO2 in a brackish tank? Are there any negative side effects? I understand it will lower the ph during the day when it is on, so I will be checking to see how much it drops by to see if that will be a problem.

I will be using:
  • Aragonite sand (raises the ph)
  • CO2 on a solenoid timer
  • Liquid fertilizer + root tabs
  • Fluval 3.0 light
  • Air stone on a timer to run at night

Plants I will be attempting first:
  • Anacharis
  • Water sprite
  • Vallisneria americana
  • Micro Sword Lilaeopsis Novaezelandiae

It is difficult to do any research on this, as few people seemed to have done it let alone post online about it. So far I have not found any reason it would be bad for the puffer or the tank. But the health of my fish is always the priority, so I am still checking if there would be any problems. Ideally I would think it will help the plants survive better in brackish, and grow faster. I am actually excited to see what happens and what plants can and can't make it.

The only thing I may have concerns about is the aragonite sand with the CO2 may cause problems. So I am still doing as much research as I can find on it.

Thanks for any advice/help in advance!
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The only thing I may have concerns about is the aragonite sand with the CO2 may cause problems.
CO2 won't impact osmotic pressure, so your puffer will be fine. No need to worry about a pH drop due to carbonic acid.

Not telling you that you shouldn't take this route but have you considered simpler methods? Like using dimmer lighting, not dosing a ton or even using CO2. Or if you do use CO2, don't run it as strongly as you think you should. If you haven't considered a more low-tech option, definitely do so. If you have, then, obviously disregard. Regardless, with a light fixture like the one you're considering, you'll be able to quickly make adjustments and switch to a lower tech option if you ever decide to.

The plants you're using aren't very demanding, so you don't really have to go high-tech. You could consider including additional hardy plants like Anubias, as they adapt extremely well to brackish conditions. I've had some Anubias for 20+ years that have moved from fresh to brackish so many times I've lost count. Have also had good luck with Cryptocoryne varieties (C. wendtii variants being my favorite) and Java Fern.
 

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CO2 won't impact osmotic pressure, so your puffer will be fine. No need to worry about a pH drop due to carbonic acid.

Not telling you that you shouldn't take this route but have you considered simpler methods? Like using dimmer lighting, not dosing a ton or even using CO2. Or if you do use CO2, don't run it as strongly as you think you should. If you haven't considered a more low-tech option, definitely do so. If you have, then, obviously disregard. Regardless, with a light fixture like the one you're considering, you'll be able to quickly make adjustments and switch to a lower tech option if you ever decide to.

The plants you're using aren't very demanding, so you don't really have to go high-tech. You could consider including additional hardy plants like Anubias, as they adapt extremely well to brackish conditions. I've had some Anubias for 20+ years that have moved from fresh to brackish so many times I've lost count. Have also had good luck with Cryptocoryne varieties (C. wendtii variants being my favorite) and Java Fern.
Thanks for the input! I originally planning going low tech/light without CO2. (and I will still do that if CO2 does not work out). This is more of an experiment to see what I can do with some brackish plants and CO2. I would also be happy with dealing with less algae if it does work out especially without shrimp/snails to assist in this tank.

Also its not that much more effort for me to add the CO2 since I am already doing it on my other freshwater tank. But I am still fairly new to this hobby, and have never done brackish before so I am always glad to learn more! My main thought is trying the faster growing plants first (that do not even necessarily require CO2), and then if those work out I can try a variety of other plants once I get through that first wave of algae that may appear since this is a new tank. I hate to see new plants I buy end up covered in algae and struggle to grow.

I have also read that Anubias can work very well in brackish, so that is good to know!
 

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Thanks for the input! I originally planning going low tech/light without CO2. (and I will still do that if CO2 does not work out). This is more of an experiment to see what I can do with some brackish plants and CO2. I would also be happy with dealing with less algae if it does work out especially without shrimp/snails to assist in this tank.

Also its not that much more effort for me to add the CO2 since I am already doing it on my other freshwater tank. But I am still fairly new to this hobby, and have never done brackish before so I am always glad to learn more! My main thought is trying the faster growing plants first (that do not even necessarily require CO2), and then if those work out I can try a variety of other plants once I get through that first wave of algae that may appear since this is a new tank. I hate to see new plants I buy end up covered in algae and struggle to grow.

I have also read that Anubias can work very well in brackish, so that is good to know!
It appears your argonite may maintain the pH of around 8..
It doesn't matter how much buffer you put into your tank, you will never get the pH to remain below 8.0 with aragonite. It's basically a limitless pH 8.0 buffer and the only way you will have an acidic pH is if you don't have an alkaline buffer in the tank. You can try to lower it with stong acids as seen in pH Down and the like, by using peat, and by using Indian Almond leaves but I can guarantee you that you won't get the pH anywhere close to where you want it and you are doing more harm than good by messing with the pH. 8.0 is perfectly acceptable to 95% of the freshwater fish and invertebrates commonly seen in the hobby.
As to CO2
This aragonite sand can be used in freshwater for keeping African cichlids. If the aquarium has enough carbon dioxide in the water, some of the aragonite will dissolve, increasing the water hardness and alkalinity.
Though when one talks calcium one should go to the saltys to really mess with your mind..


How to Set Up (and Maintain) a Brackish Tank | Step-by-Step Guide

Plant choices seem hit and miss..though acclimating seems a wise choice..
 

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I have never had a brackish tank before but I have given real thought to trying one. Your salinity will probably be the major determining factor for plant survival. Go too high and everything will die even though you will still be in "brackish" territory. So I would run things on the lower range of happy for your puffer.

If you live near a bay or estuary with brackish water, I'd give serious thought to seeing if you can go for a hike and collect some plant cuttings or find plants washing up on shore after a storm. There are species that only live in brackish environment that are simply not in the hobby because brackish tanks are so rare.

I think CO2 will be fine in brackish. This is based on people using it in saltwater tanks for growing seagrass and/or macro algae. If it works there it should work the same in a brackish tank.
 

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Like using dimmer lighting, not dosing a ton or even using CO2. Or if you do use CO2, don't run it as strongly as you think you should.
This is what I'm doing now - what George Farmer would call medium energy - in my 2 40g aquariums. One has been running since Dec and is doing very well.
 

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I think saltwater photosynthesizers usually get their carbon from carbonate, not carbon dioxide. Maybe brackish plants will be able to harvest carbon from the carbonate and you won't need to supplement carbon dioxide?
 

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I think saltwater photosynthesizers usually get their carbon from carbonate, not carbon dioxide. Maybe brackish plants will be able to harvest carbon from the carbonate and you won't need to supplement carbon dioxide?
One night, later than I should have been trying to read something, I came across a paper which was written to talk about plants using carbonates as carbon sources. Being as late as it was I promptly went cross-eyed and turned it off before I had really gotten much out of it. There is some info online about this, but sadly I haven't really done any more research into it.
 

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One night, later than I should have been trying to read something, I came across a paper which was written to talk about plants using carbonates as carbon sources. Being as late as it was I promptly went cross-eyed and turned it off before I had really gotten much out of it. There is some info online about this, but sadly I haven't really done any more research into it.
I probably know less about it than you. A basic google search suggests Vals and Crypts can use bicarbonate as a carbon source (this makes sense considering how Vals can grow in the African rift lakes). I believe Anubias are know for this too?
 

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Saltwater plants are known to use carbonate as a carbon source when nothing else is present, but they prefer co2 and will switch to it when it is available. This is from the saltwater forums and a brief writeup on growing seagrass. Apparently when saltwater plants are using carbonate it changes the parameters enough that its detectable, so when they introduced co2 they could tell the plants switched over to it.
 
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