I've read more than once that surface agitation is a detriment to CO2 levels in the tank. I notice if I do not run the skimmer I get a bit of a film built up on the surface and it seems my angel fish is more inclined to go to the top and gulp as if needing air. Am I killing my CO2 levels by skimming? Is it not recommended?

I don't see how skimming affects the rate at which CO2 leaves the water, as long as the skimming doesn't ripple the surface excessively. My constant water change system skims my surface constantly, and I have no trouble getting to 30-40 ppm of CO2 in the water. I do think I run a higher than usual bubble rate doing so though. If I had DIY CO2 that might be a problem.

Actually...... it's highly recommend.
By most anyone that does a lot of tanks. ADA uses them on larger tanks, his giant tank has them.

I have them.

CO2 is easy to add, you just add a bit more than without surface movement.
The real benefit is the exchange of O2 and better mixing.

I like lots of current and mixing, it's good for plants and reduces algae. There's a lot of evidence of that both in FW and marine systems.

It helps exchange nutrients as well as CO2.

In most cases, like yourself, folks reduce their surface movement and flow down too low. Their fish gasp.
Many blame the CO2.

It's mostly the low O2.

If the plants are growing well, that can off set that*(but only during the day, earyl am, they gasp), if you have few fish, that also can off set that.

If you have good surface movement, etc, then you lose some CO2, so what, it's cheap and you just turn the needle valve a 1/16" of a turn etc.

That way there is plenty of O2 and CO2 and the tank is well mixed, the CO2 is not allowed to build up as much this way and the O2 is not allowed to get too low.

So it's a mix of 3 things really, not enough plant growth/low O2(both plant growth and surface exchange) and too much CO2.

I've found it easier to maintain a stable level of CO2 ina high flow tank, less fish issues and better long term results.

Some folks enjoy suggesting surface movement is bad.
That's rubbish.

You can go over board and make it a torrent, but some slight rippling is fine.
Or if the degassing exceeds the CO2 diffusion system's capacity (that is often what happens and folks complain they cannot get enough CO2 into their tank etc)

When you use a skimmer and over box, and a wet dry etc, you should raise the level in the weir box to about 2-4" drop only.
No more.

The wet/dry bioball tower needs duct taped up so no air exchages in there.
That solves about 95% of any issue.

Regards,
Tom Barr

Good to hear, or read that is. I've been skimming for over a year but I do it with a canister filter so there is no open sump box to worry with. I also felt it was much better to skim so that I would be constantly exposing water to atmosphere to absorb O2 as needed and eliminate any worries with the fish. Everyone keeps telling me that the most likely problem I have with growth is low carbon so I'm trying to increase levels by adding more and/or decreasing loss. My Red Sea drop check should be arriving today so I'll be mixing KH solution and getting that setup tonight and finally have an accurate reference for CO2 levels in the tank. I've noticed links to several threads on preparing KH solution and setting up the drop check to measure CO2. Would someone be kind enough to point me toward the thread that is most recommended. Thanks...

I'm goading Vaughn into a nice article like synopsis

That way we can arrive at some consensus about what to do.

Two vendors on both sides of the pond will sell the KH reference solution diluted down etc perhaps.

Using Bromothymol blue is the best alternative and the vendors should be able to get this in large amoutns as well as small 1 oz sizing as well.

You add 3 drops to 6mls of KH reference solution basically.

Regards,
Tom Barr

But how do I prepare a KH reference solution correctly? Will the Red Sea unit come with Bromothymol? If it does not come with it should I order some seperately or can I use whatever it comes with? Thanks...

As far as I know all pH test kits that measure pH from about 6 to about 7.2 use bromothymol blue, so you can just use your pH test kit reagent.

Mix 6 grams of bicarbonate of soda (baking soda) into 1 liter of distilled or DI water, giving you 200 dKH water. Then take 10 ml of that and mix it with 490 ml of distilled or DI water to get 4 dKH water. Add enough of this water to the Red Seas CO2 Indicator to fill it to where they say it should be filled, and add 2 or 3 drops of pH reagent to that, to get a good, easy to see blue color. The amount of the reagent you use isn't critical at all.

Vaughn, thank you so much for that simplistic explanation. I was trying to read this thread - Making Standard KH solutions - Making Standard KH solutions - and nearly went insane. Do you happen to know of a lab supply where I can purchase KH standard that is cerified like Tom mentioned? I will make it the way you have instructed until I can source a supply, but a certified standard would eliminate any mistakes I may make from the equation.

Don't worry about mistakes right now. Use your KH test kit to see if the batch of 4 KH water is close to being that per the kit. If you are off even 20% it is still better than what you have now.

If you don't have a scale capable of measuring 6 grams accurately, you can mix a little baking soda into a liter or so of distilled water, check the KH of that with the test kit, and if it is very high, dilute some of that water about 4 to 1 with more distilled water and repeat the KH test. Once you get a KH that you can measure, you can dilute directly to 4 dKH using the dilution equation Tom provided. It will only be as accurate as yout test kit, but still that is better than any other method you now have. In a few weeks we should be able to buy the water already mixed and done accurately.

Yes, the 4 KH solution in 500mls amounts will be sold for about 8.99$. Should last several years. The pH indicator will run about the same and also last several years.

Regards,
Tom Barr