Am I getting an accurate CO2 reading?

[Eric_Dyer]

Hello, new to the forum and hobby, and love this resource! I have a 90 gallon tank fairly extensively planted with vals, java fern, micro sword, various annubias, and diandra. Lighting is through two double 54W T5 fixtures (216W total).

I wasn't getting the growth I wanted and have been fighting algae, so over the weekend I set up a pressurized CO2 system. It's basically just set at a hair over 1 drop per second, and running through a Red Sea Reactor 500 box. So, after all that, my questions:

I took KH and pH measurements last night (API liquid kits) and had the following readings:

pH: 7.1
KH: 11*

We do have very hard water, but I have no idea if that was too high or not. I then pulled about a cup out and left it to outgas for about 16 hours, and today took readings on that:

pH: 8
KH: 11*
GH: 21*

And, finally, just did our tap water:

pH: 7.4
KH: 11*
GH: 19*

So, I guess my question is, does that all jive? More specifically, based on those readings would you guess the KH/pH method will give me accurate estimates of my CO2 levels, or does my tapwater likely have characteristics that are inflating the KH number?

Thanks, and sorry for the very lengthy first post!

 

[phanmc]

The pH/kH chart is only accurate if CO2 is the only acid and carbonates is the only buffer in the water, in an established tank this is never the case.

Invest in a drop checker, you can find them cheap on eBay or places like greenleaf aquarium, which isolates an indicator solution so only CO2 affects the reading and will give you a much more accurate reading.

 

[Eric_Dyer]

Thanks - definitely have plans for a drop checker. In the interim, though, would the KH have dropped to 3.3 after outgassing if there were other buffers elevating the reading from the tank?

 

[VaughnH]

The KH shouldn't drop at all, but if the water, after sitting out over night had only .3 ppm of CO2 left in it, and it had 30 ppm in the tank, the pH would go up when outgassed by 2.0. That's the flaw in the outgassing overnight method for estimating CO2 concentration - we have no way to be sure how much CO2 is in the outgassed sample. The commonly accepted 3 ppm is just someone's guess, based on wishful thinking, as far as I know. My testing showed much less CO2 if you let it "outgas" long enough.

 

[Eric_Dyer]

Oops, I mispoke/omitted part on the second post. What I meant to say was the the readings for what I left over night to outgas came out to 3.3ppm CO2 (not 3.3* KH), but the stuff right out of the tap calculated as around 13. It all may be moot, though, because I took phanmc's advice and ordered a drop checker today. I'll just keep using the table method until it gets here.

A couple of other questions, one related, one totally unrelated, but I'll go ahead and post both here. I ordered one of those Cal Aqua double drop checkers because it kind of made sense to me, but since I have no idea what I'm doing I don't know how well they actually work in practice. Any thoughts on them?

My unrelated question has to do with my lighting - I was told that T5 HO fixtures don't correlate directly to T8s on a wpg basis due to higher PAR values - any thoughts on what 216 watts T5 translates into? (If I should post this in another forum just let me know!)

Thanks for all the help!

 

[SuperColey1]

For ease (IMO) you can virtually assume a T5 is going to be twice as effective as T8 due to penetration, efficiency and intensity!!!

216W of T8 would be high light on your tank so you can guess how high it will be with T5.

This is going to mean you will need superb filtration/flow, perfect CO2 and ample dosing.

It would be best to reduce the lighting down to 1WPG for most of the photoperiod and just use the rest for a 'noon burst' if you want to as that amount of light over a large tank is going to be very hard to keep 'on target'

AC

 

[VaughnH]

I have one of the CalAqua double bulb drop checkers too. It works fine, but I was eventually disappointed in that I still have trouble judging the colors. Also, I found that cleaning it was a nuisance, and maintaining both solutions was more than I wanted to do. So, I went back to the standard one bulb unit.

Don't expect the drop checker to give you the last word in how much CO2 is in your water. At best, it gets you close to a good concentration of CO2, avoiding the problem so many of us had, where we had 5 ppm and were sure we had 30 ppm, and were afraid to try to increase it. With the drop checker you will at least know that in the area where it sits, you probably have 20-45 ppm when the checker is green to yellow-green. But, then you need to increase the bubble rate a small amount, wait a day while watching the fish every hour or less, to be sure they are not adversely affected, and watching the plants for good pearling. Then, repeat this another day, etc. until the plants pearl good, but the fish don't show distress - meaning they don't all cluster at the surface like they are trying to breathe air, and don't have their colors fading out or are laying on their side on the substrate, swimming oddly, etc. When those things happen you are on your way to killing them with the CO2.

 

[Eric_Dyer]

I have one of the CalAqua double bulb drop checkers too. It works fine, but I was eventually disappointed in that I still have trouble judging the colors."

You've sure got that right - I'm not sure the second bulb helps at all, really. I have to stick a white plastic spatula behind it to get any kind of reading. Not sure why they opted to include that white plug in the reference solution but not in the indicator. Or better still, why they don't just make the whole back side of the indicator white. I'd love to find a unit that is glass on half and white plastic on the other other half, in kind of a clamshell design.

Regarding the maintenance of the reference solution . . . since it's inert and sealed, does it ever really need to be changed?

 

[VaughnH]

I have one of the original two bulb Cal Aqua units, and mine does not have the reference solution sealed, nor does it have any white plastic anywhere. I asked them if I could add more pH reagent to both solutions to make the colors easier to see, and they agreed that it would be OK to do so. So, I was adding an extra drop of pH reagent to both bulbs.

Both use bromothymol blue as the indicator dye, and, being an organic dye, the color will not remain the same for a long time. It appears to me that after a couple of weeks or less, the color starts to fade a lot. That is why I think replacing the solutions weekly is a good idea.