Backyard Aquaponics
A place to discuss aquaponics

The pH of my tap water is very high... it's off my pH chart and I think it's probable close to 9.0. The water where my fish came from is the same (tap water comes from that river) so it's ok for the fish but not for the plants. My alkalinity is 6 dKH (2.14 meq/l). I've gotten the pH down a bit by adding vinegar (slowly!) but there was still a large pH shift from the morning to evening because of algae in the tank. In the mornings it's near pH 7.8 and then during the day and towards the evening it climbs over 8.0 up to 8.1-8.2. As the algae sucks the CO2 out of the water during the day it causes the pH to climb. At night as it sucks up O2 and 'breaths out' CO2 the pH lowers again.

I have a chart in my testing kit that lets me line up pH and dKH and it shows that the CO2 content of water is pretty low in the first place. So I got some of my brewing equipment out. Filled a 2.5 gal carboy with sugar water and added some yeast. Next thing I did is attach an airline to the carboy and put the other end of the airline in some rockwool (to serve as an airstone to break up the bubbles) and then shoved the rockwood in a small 2" long piece of 1" pvc.

And how it works! The pH of my water has dropped down to 7.6ish and stays there for the entire day. My alkalinity has stayed at 6 dKH (2.14 meq/l) I've had it running in my system for 3 days now and everything seems to be fine.

I do have a few concerns though. The CO2 I'm pumping into the water... the algae in my tank seems extra green hehe. I've tried to introduce some duckweed to shade the water but the two goldfish I have in the tank with the sunfish are eating it all. Am I just causing a bigger algae problem?

Another thing.. the water I'll be topping the sytem off with is the same 9.0 pH tap water. So I figured I'd stick the CO2 bubbler into a 55 gal drum full of water over night. OMG it dropped the pH below the bottom of my testing chart (7.4) and appears to be a lot lower then the lower bounds of the chart. The tested water turns pee yellow whereas the bottom of my chart is a yellowish-green. It also seems to have lowered the alkalinity a lot (down to 2dKH I think it tested). Is the CO2 bonding with the calcium carbonate and precipitating it from the water?

oh yeah, i had a question as well.... will the additional CO2 in the water help the plants in the growbed out? I know that they take CO2 in through their foliage but I've also read that they take some up via their roots. What do ya'll think?

I'm not sure about the answers to some of your questions. For Hydroponics, people will sometimes use CO2 into the air during the day to promote plant growth. At night the plants and algae tend to strip O2 out of the water/air so I would say adding CO2 at night could cause problems. Most people want to add more O2 to the water under normal circumstances.

The CO2 is probably promoting Algae growth during the daytime.

Duckweed is a fav food for many fish so trying to use it to shade out algae in the main tank with the fish could be tricky.

You might wish to add shade over your tank to help against the algae.

How mature is your system? Has it finished cycling to the current load? I had been expecting my tap water to have plenty of buffering capacity but as it finished cycling, the pH dropped and I started adding shell to keep the pH up.

sorry for not reading this sooner.

yes co2 will lower the PH of your water and increase the KH also.

but it is temporary. effect will reverse unless constant CO2 is bubbled in.

is commonly used for aquariums with aquatic plants but would be of little use with terrestrial plants imo

As your system matures, it will naturally pull the pH down. If you did frequent small water top-offs, then new water would not tend to raise the pH much, if at all.

Another alternative would be to use rainwater. Can you collect it off your roof or something?

I've had the system set up for maybe 3 months now with about the same number of fish in it. The load is really low.. I've got 2 large goldfish and 15 assorted sunfish (bream) ranging from 1"-2" with one 3"er in there. They're in 300 gal tank with 150 gal of grow beds so there's really not that many nutrients. I've never noticed it cycle... I've never measured any nitirite, ammonia or nitrate in the water. I have tested (a lot) but the nutrients never measure and never have. I really need to go catch some more to stock it denser.

I've also been keeping up with the O2 in the water, especially since I've been adding CO2. It hasn't gotten below 4 mg/l at an time and it's usually closer to 6 mg/l. (morning/evening of course)

I could collect a little bit of rainwater but i dont have big enough barrels to keep it in. in the spring we get plenty of rain but during the summer it could go a couple months without anything worthwhile. You're probably right about the water top offs not effecting it to much. Might even be good if the system starts heading to the lower pHs by itself.

steve, you say it will raise the KH? That hasn't happened in my system but in the 50 gal barrel I actually lowered the KH (from 6 to 2!) To be honest, I didn't take a baseline reading of the tap when I first put it in the barrel.. perhaps the city was pumping really low KH water that day?

you got me paranoid!

but i checked and yes, i was right

see table half way down

http://www.cichlidchick.com/pages/kh/kh.htm

PS i think you will find it hard to maintain high co2 and high o2 via airstones.

give it away imo

?

That table says:

Ways to Lower KH => "Injecting carbon dioxide (CO2)"

That's what I read as well.

I have been paranoid of my O2 levels but I've been testing them (twice daily sometimes) and they don't seem to be changing much. My pH isn't going down past 7.6 so I think the CO2 must be getting bound up and will continue till there's no more buffer left, right? I copies this formula from another site... it's for bubbling carbon dioxide through limewater. I'm guessing it's the same reaction that's going on in my system?

1. CO2(g) + H2O(l) --> H2CO3(aq)

2. H2CO3(aq) + 2OH-(aq) --> CO32-(aq) + 4H2O(l)

3. Ca2+(aq) + CO32- --> CaCO3(s)

Chemistry was one of my nap classes.... Now let me see if i have this correct.

1. Carbon Dioxide (CO2) is injected into the water (H20) and forms Carbonic Acid (H2CO3).
2. Carbonic Acid (H2CO3) is neutralized by the lime (?) in the water and produces a carbonate ion (CO32).
3. Calcium (Ca2) bonds with the carbonate ion (CO32) and forms Calcium Carbonate (CaCO3)

So as long as I have a buffer my pH shouldn't drop to far? Also, as long as I have my buffer the water shouldn't get over saturated with CO2 either... umm right? And as long as the water isn't saturated with CO2 it shouldn't effect the amount of O2 that can be dissolved in the water... please?

Alternatives I guess.... if I could get rid of the algae then I wouldn't have the high pH problems because the algae wouldn't be taking all the CO2 out of the water. Also, if I had a higher density of fish they would be putting their own CO2 in the water, especially during the day when they're most active and it's most needed to offset algae CO2 takeup.

Maybe I'll keep the CO2 generator in place until I've got more shade and fish. It seems the safest way to keep my pH range in a place where my plants can actually take up the nutrients. If I quit then my pH will skyrocket during the day and the algae is the only thing that will be taking up the nutrients. Since I've gotten the pH down my plants are starting to look healthier too.

I hope this post doesn't sound to schitzophrenic, was written i pieces.

Similar to a previous discussion... don't know if it'll help clarify

viewtopic.php?p=112814#p112814

OK I got nothing to add except I just use hydrochloric acid from a pool shop instead of vinegar.
You probably shouldn't though unless you know what your doing.
Its a really easy way to kill your fish, plants and self if you stuff it up.
But its cheap!

lols

If you have your water buffered it is difficult to disolve much CO2 in there. If your water is being disturbed to ensure good oxygenation, then it will be difficult to keep disolved CO2 in there as it will 'degas'

lol, look at the time i posted my orginal! thats MY excuse.

have heard vinegar (acetic acid) is not a good choice as rebounds can occur due to intermediate compounds