fig 8's and water hardness

[crazy loaches]

Because I am considering attempting co2 injection in my mild brackish tank, I am looking at the possibility that the aragonite is going to be releasing calcium and perhaps other things into the water. Do fig 8's prefer hard water? Does anyone see any potential problems? I also have BBGobies in there too.

[Nick]

Most brackish fish enjoy harder water, as long as it's not excessive. I think the figure 8's would like it.

[Boxermom]

I can't remember where it was but I read recently from experienced aquatic gardeners that CO2 injections in brackish tanks is useless.

[Peregrine]

My current fw tank used to be a brackish tank with argonite/gravel substrate....from personal experience...it is really hard to get CO2 Levels up to prefered levels, or aleast it is difficult to get an accurate reading due to the high PH/KH

I dont know if it is useless, but the buffer seems to cancel out the carbonic acid reaction with the PH, so it may just be that it is not testable...But I have neither the scientific mind or experience to prove or disprove that.

[RTR]

The best test technique requires you to aerate a tank water sample for some fixed time (I used 30 minutes), and compare that final pH to the tank pH. It is not perfect, but better than most other test protocols.

IMHO & IME, the f-8 will do better in high GH/KH water than in the same specific gravity with lower GH/KH, but I do not have enough data to prove it.

[kjharve]

There have been a couple of posts on this lately. If I find them I'll post them. I remember a lot of people commenting that CO2 is pretty useless in a tank, especially if there is a lot of surface agitation as the CO2 will simply disappear.

Another post mentioned that F8s in the wild are found in fresh but rather hard water, if I remember rightly. Brackish water has been found to be the best way to keep them in aquaria but I certainly don't see hard water causing them any problems at all. As with everything though, there's always a limit.

What's your motivation for this? I'm guessing its something to do with plants. What fertiliser do you use?

[RachelS]

Once the sg gets to 1.005, very few plants do well I've found and read. Mangroves are about the best but need an open topped tank which is a no no with puffers. I think the CO2 would be wasted and you'd end up with a fair bit of algae

[RTR]

CO2 does not promote algae, but I agree it is wasted on emergent or ememrse plants - they get CO2 fron the air.

[crazy loaches]

Hold on a second I think this is all going off on a tangent CO2 is extremely beneficial to plants and is almost required in heavily planted tanks, and is the best deterrent against most algea (when the plants are flourishing in it anyhow). It shouldnt be too hard to measure, there are a few methods but the best method is reading the fish and the plants.

I dont see how it can be wasted just because the water is brackish. Unless somehow the salt blocks the uptake of co2 or something like that? And yes, I am aware of what plants do well in what SG (there is a sticky on that). Surface agitation will surely off-gass CO2, thats why I dont plan on having surface agitation (except at night when I will have agitation).

No emergent or emersed plants, just submerged.

The original question was about the hardness preference of Figure 8's and if anyone happened to know what would happen with aragonite and co2, that is if it would start to dissolve and release minerals into the water. I am hoping what RTR said in response is accurate, as I will probably be trying this

kjharve - yes the motivation is to grow plants, which need co2 to thrive. I am just not sure how the co2 will react with the aragonite. As far as fertilizers I use dry ferts from greg watson (gregwatson.com) and dose the EI method in my main FW plant tank. My plant mass in this brackish tank isnt enough yet for EI, nor is the plants carbon requirements being met (I dont beleive anyway) so i am dosing around 1/2 the amounts of EI.

[Pufferoni]

I just planted my F8 tank this weekend so I have been doing some research. There seems to be some belief that calcium substrates do dissolve at a higher rate with the C02 and that Co2 and stronger lighting is important to the overall heath of plants in brackish tanks when compared to the same plants in fresh.

I opted for flourite and sand substrate. I can not back up these observations with any science as I am new to both planted and brackish tanks. I might be able to come up with some links if anyone is interested.

The bottom line might be as you suggested let the health of the fish be your guide.