# How test for CO2 when think phosphate must be high?



## kclendinning (Aug 29, 2005)

Hi,

I've tried to grow aquarium plants in a 20 gal tank for almost a year now. Sometime during the year, the plant goal was put on the back burner, and I concentrated on the fish.

Recently I thought I'd try to figure out the plant situation. I had decided my problem was my substrate and lack of substrate heater, and thought I'd use this as an excuse to upgrade to a 65 gal tank (3ft x 2 ft x 2 ft high - on order). Ultimately I think I might want a planted discus tank.

In doing my research, I finally stumbled on this site. THANKS for the posts - they've helped.

I now know that my problem is most likely lack of CO2. I had thought about going that route, but the local store steered me into a new light, and some plant fertilizer to be added when water is changed.

So, tonight thought I'd verify my CO2 is low. I used the website: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

According to it, the CO2 is at 28! 
pH 7.2
KH 15

According to that site, I must have some phosphate in the water. One of my recent "solutions" for my plant problem was to add Discus Buffer to the water to bring the pH (8.0) down. (I have done one water change since Discus Buffer was added) I suspect that has influenced the 28 number above. Previous KH tests have been at least 12 or higher. (Though my pH has been high too). I don't have a way to test for phosphate (yet).

Finally my question, how does one test CO2 level if the water 'normally' has phosphates in it? If I get a CO2 system, how will I know it isn't too high, and/or that it's working?

Thanks in advance. Also, if you don't mind, here are my plans for the new tank. I think I'm still going to get it, as I've thoroughly enjoyed doing this research. I'm seriously looking forward to figuring out what plants to get and how to lay them out. I keep having this vision of all these plants growing in the tank....

On order: the 65 gal tank, 
w/ 2 compact florescent lights 55 watts each. 
substrate: 4 20 lb bags of eco-complete
ordered a substrate heater, but plan to return it
CO2: considering getting the complete CO2 system @ Foster & Smith. 
10 lb carbon dioxide tank, maybe 5(?).
Heater - whatever the local store recommends
Filter - not sure, was going to see what local store suggested, but am wondering if canister would be better. I've read in books that you might want to have the return valve below water level (reduce amt of O2 (?) in the tank??? The hang on filter I have now drips water in, and I have no way to adjust the rate at which the water is returned. I don't know if that's true for all hang-on filters or not. I also get confused as then what about the biological portion of filtration (will the plants be enough)?


Plants- easy ones! I have a little bit of sag (grass like foreground plant), and an anubia barteri

Fish: (once tank established) - community tank - some cardinal or neon tetra, harlequin rasboras (maybe?), corys, and my current "brood" (4 rams, a growing pleco, 2 clown loaches & a black phantom tetra). (The concept of a Discus tank is a "future" thing - want more confidence & experience before I attempt a discus.)

Thanks in advance for any answers & advice 
kc


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## SnyperP (Dec 10, 2004)

Normal amounts of phosphates will have a negligable effect on the PH. Phosphate PH buffers changes the PH with high loads of phosphates. I'd recommend discontiuning the buffer. If you're planning CO2 injection, that will naturally bring down your PH. Generally, the higher your KH, the less it will actually go down. Like you mentioned before, a kh of 15 and an ideal 28-30ppm of co2 will get you to 7.2PH. If you need to go lower than that, you can cut your KH by using some RO water. A ratio of RO to tap will take care of that.


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## Laith (Sep 4, 2004)

Yes, discontinue the Discus buffer... it is invalidating your CO2 calculations and is not necessary.

Some other comments...

- Definitely get a cannister filter.
- With the addition of CO2 you will need to fertilize the tank with macros and micros.
- You have nowhere near enough plants. You need to heavily plant the tank from day one, preferably with fast growers initially.

HTH.


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## shalu (Oct 1, 2004)

Use multiple, smaller heaters, say 2x100w. One big heater goes wrong and you have yummy discus soup.


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## billionzz (Apr 9, 2005)

Your CO2 measurement is off (because of the buffer) and save yourself some money by not buying the substrate heater. The plants will grow fine without a substrate heater.

Bill


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## HeyPK (Jan 23, 2004)

Do your CO2 test on two samples of water, one just taken from the tank, and the other taken and allowed to stand in an uncovered dish or bowl for 24 hours. In the second sample, the CO2 will diffuse out until the sample is in equilibrium with the room air. Water where the CO2 is in equilibrium with the atmosphere has very little CO2 to support growth of most aquarium plants. You can consider the CO2 content to be essentially zero. Subtract your CO2 reading from the 24 hour sample (which is mostly due to the phosphate content) from the CO2 reading from the just-taken sample, and you will get a good idea of the actual CO2 content.


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