Getting the coverted 25ppm of CO2

[cdelucia]

I’ve been having more success with my planted aquarium in the past 6 months but still have to come to grips with a few water parameters. I use DIY CO2 (two 2L bottles – make a new one every week which is a way to stagger and thereby keep a more constant amount of CO2) as well as PMDD. I’d like to have a CO2 level of 25ppm and a pH of 6.8 as well as a KH of 5.3. As I start to lower the pH through increasing the amount of CO2, things become vary close to what I want. Within a month’s time though, the pH is at 7.6, KH is 5.6 and the GH is 10.6. I’ve heard about buffers in passing but really haven’t paid much attention to using them. Can someone please give me a crash course or point me to a more in depth article on KH and GH buffers, their relation to pH as well as a good brand for planted aquariums (I hear some us Phosphates and I find keeping those down to 1ppm really cuts down on the BBA)?

Also, I've been trying to get my NO3 levels up (20 ppm preferred) but to no avail. Week after week it stays at 7ppm. Fe on the other hand is getting precariously high at 0.4ppm. I've tried adding 3/4 tsp more KNO3 than called for in my PMDD batches but that doesn't seem to work.

It should also be noted that I do have a rather large piece of driftwood in my setup. I hear that can cause water hardness. Also, does floating plant debris (leaves) cause fluctuations in the KH/GH? I usually strain these out once a week.

My aquarium is a 29 gallon with 5 cherry barbs, 4 gold barbs, 4 cardinal tetras and 3 SAEs (which are getting quite big). I feed them flake food pretty sparingly so there's little uneaten food to spoil the water. I've got two 65 watt 6700K/10000K lights and an external Fluval 204 filter. I keep the lights on a good 10 hours a day.

[cdelucia]

Um, can I bump this in the hopes of getting some sort of answer on achieving the covetted (and steady) 25ppm CO2?

[grey_fox]

Hey there,

I was also mystified by this magical 25-30ppm of CO2 and have gotten the hang of it after some discussion with PeterGwee from this forum. You can read the entire thread at the following URL; http://www.aquaticquotient.com/forum...ad.php?t=20581

Hope it'll help you as much as it helped me.

[cdelucia]

Thanks, I shall check it out.

[|squee|]

If your plants are growing well and taking in all that nitrate, I wouldn't be surprised to find it at 7ppm week after week. Have you measured before-dosing, after-dosing and in-between?

Floating plant debris shouldn't affect kH/gH/pH fluctuations that much. Furthermore you are skimming them out weekly. Your driftwood may be lowering the pH with its tannin leakage, therefore you cannot rely entirely on the kH/pH chart measurements for CO2 concentration. That chart requires that pH be affected only by CO2 addition and nothing else in the tank.

Controlling CO2 will not be easy; if I am not wrong, keep it as high as you can and as stable as possible. Perfection is not possible, therefore one must keep on top of things daily (check plant health).

I don't think keeping phosphates down to 1ppm keeps out BBA, it is more of a CO2 issue in CO2-enriched tanks.

[cdelucia]

So, I get the distinct impression that I shouldn’t worry about specific amounts of KH (though I must still pay attention when using a CO2 chart).

Currently I’m piping my CO2 into the filter intake. With such bright lighting, I have to infuse a lot of CO2 into the water as quickly as possible. I guess you could say I have a high maintenance / high growth tank (just at a DIY budget/approach). As a result, I get gluts of undisolved CO2 which occasionally belch out of the filter output spout. This is understandable: the filter isn’t made to be a CO2 reactor/diffuser). I was wondering if anyone knows of a good diffuser that is small – I’m trying to keep my setup as a walk-around one (as opposed to a “front-only” view). I’ve seen some in catalogs and online and am not sure what kinds of pressure they need to work properly (again, I have 2 DIY bottles of CO2 here)? I’m not too keen on getting an external reactor/diffuser as I stink at plumbing (if I were to run H2O from my filter to the reactor and back) and am not too keen on having it on its own circuit (with it’s own water pump, etc.).

Any suggestions?

[|squee|]

I think your impression is right. A better way of measuring CO2 concentration will be through plant growth and fish reactions throughout the day, but measuring CO2 will be pointless imho because you are using a DIY system where you can't control the CO2 input. You can only fine-tune it such that it gives out the maximum yield and stabilizes in output rate. I like to think of the CO2 chart as a way to get a estimated concentration of CO2 in my tank, then fine-tune that to suit my individual tank's needs by visual observation.

Have you seen Tom Barr's internal reactor? You can run it from your filter output instead of having to use a powerhead for it.

A diffusor will be a good option; when I was using DIY CO2 I was using diffusors. I don't know why people say that you can't get enough pressure... I was doing fine. Get the ADA range from www.adgshop.com if you live in North America, or try other brands.

[cdelucia]

Well, I'll have to look into how to use the filter's output head to do the diffuser thing.

My GH has now gone up to 12 degrees. Should I be worried about this? Should I get something to bring it back down to a lower level? Can it get this high by fertilising too much?

My pH is still 7.5 (despite increased bubble rate) and the KH is 6.4 degrees. After reading the thread noted above (about getting enough CO2), I'm pretty certain that the CO2 is just collecting in the top region of my canister filter and then being "belched out" on occaision and promply escapes out of the tank into the atmosphere. Even with that, you'd think it would be enough contact with the water to be absorbed into it. It probably is, just not enough of it is in contact with the water (probably in a big bubble near the top of the filter).

[cdelucia]

Well, I've been looking at the venuri posts at Barreport.com and haven't seen anything about using the filter output nozzle (er, fixture-thingy) and part of the venturi diffuser. Then again, even if I was successful in doing that, CO2 would be too high at night as the filter is obviously never turned off.

I'm hoping to build a fairly small venturi this weekend - the lack of CO2 absorbtion is my biggest problem right now. I have a feeling that will bring the pH down to a good level. I'm just wondering if I can get it to stay down long-term.