Inline diffuser injection method query???

[Ady34]

Hi,
after reading a lot of recent posts regards ph readings pre and during the photoperiod to determine co2 concentrations it got me thinking about injection methods....
I'm currently using an inline atomiser, which by all accounts is aimed at supplying a 'mist' of co2 to the plants for direct leaf contact and uptake. In which case does it really matter about the ph readings (in relation to co2 availability) as its not the dissolved co2 that the plants are accessing, but actual micro bubbles? The injection rate and distribution will be exactly the same regardless of duration it is on for. Can you simply turn co2 on just prior to the photoperiod, saving gas and the time in which fish are exposed to high levels of dissolved co2? During the injection and photoperiods, gas will naturally dissolve to supply the needs later on when the gas is switched off, so maybe that means you could also shorten the injection period further as long as there was a lot of mist contact at lights on.
Taking ph readings will be useful in determining safe levels for the addition of fauna, hourly measurements tracking the ph to ensure no greater than a 1ph drop which should be somewhere near 30ppm tolerance. Then watching the plants to see if you need more/less, lighting adjustments etc. Drop checkers seem pointless in a mist tank as they will give inaccurate readings.
Is this reasonable or am I missing something obvious......do we want mist and dissolved gas?

Cheers
Ady

 

[Tim Harrison]

Wow...I think you've just come up with the basis of a PhD thesis Does direct adhesion of CO2 micro bubbles to a relatively small surface area reduce the unstirred layer thickness to the degree that CO2 absorption is greater than that of dissolved CO2 over the entire plant surface? Or some such...etc

Your supposition certainly seems rational. But I suppose, as you say, any experiments would have to be empirical since it would be very difficult to quantify, not least because I would imagine mist and dissolved gas are mutually inclusive.

 

[Ady34]

Ha, im sure there has been much discussion on the different types of c02 injection and the results. On reflection im sure if it were viable we wouldnt be consistently given advice to turn c02 injection on 1hr pre photoperiod, i suppose the theory of inline diffusers still is most effective as more bubbles make contact, which they will over a longer period so a period of gas injection pre lights on allows the micro bubbles to build up on the leaf.....maybe i had brain freeze yesterday night

 

[Ady34]

Good question!

Most inline diffusers are designed to be place on the outlet, so the CO2 microbubbles or mist can be distributed effectively throughout the water column. CO2 like this, in its gas form, is more efficient at delivering CO2 to the plants. It also means that one can run a comparatively lower dissolved CO2 level in the aquarium, yet still obtain enough CO2 for the plants.

However, this method does require excellent water circulation in the aquarium to enable the CO2 mist to reach all parts of the tank and plants. In poor circulated tanks some plants will be getting plenty of CO2, others will starve and algae will proliferate.

I have noticed that in tanks with lower levels of circulation it's better to have the CO2 100% dissolved. It seems that the CO2 is more easily distributed this way, and all the plants stand a better chance of getting their required CO2.

This assumption is based on experience with various set-ups and differing CO2 delivery methods, from ladder diffusers, to ceramic discs placed at the opposite end to the filter, to inline diffusers place on the inlet and outlet.

For me the hobby is more about aesthetics than pure plant growth and gardening. So I have an inline diffuser placed on the inlet. This means I don't get millions of white bubbles all over, spoiling the aquascape. The trade-off of this vs. risk of the filter leaking (I haven't had an issue in over 7 years of CO2 being pumped directly into filters in one way or another) and better plant growth is worth it, in my experience.

So, in summary; if you want the best possible plant growth and have excellent water circulation, and don't mind seeing lots of bubbles floating about, then positioning your inline diffuser on the outlet is the better option.

If you want 100% CO2 diffusion and no bubbles then the inlet is an option.

Quick search of the forum and BOOM!
Maybe i was correct in my thinking


Note to self....practice what you preach and use the search function. Slapped wrist

 

[Tim Harrison]

I remember reading George's assumption a while back, and again it certainly seems rational to a point. As I understand it good circulation, as opposed to good flow, will be needed to disperse the mist ubiquitously to ensure all plants get enough CO2. Good flow on the other hand reduces unstirred layer thickness and will possibly increase the absorption rate of dissolved CO2. That said in the absence of scientific evidence George's assumption perhaps remains more to do with aesthetics than actual CO2 diffusion. Nevertheless, your idea, I think, is to take it one step further and to actually try and gauge the minimum duration and rate of CO2 mist needed for optimum plant growth and see if it's less than when using dissolved CO2 alone. I for one would be interested in your observations.