solenoid or not?

[mike b]

Hi all. Just wondering how many of you turn your co2 off at night and who keeps it going 24/7? I see advantages and disadvantages to both. It's commonly said to turn co2 on 2 hours before lights on to get co2 levels to optimum as plants need most of their carbon soon after lights on. But is this not too much of a pH drop in a short time? If we have a very low level of co2 as it has been turned off all night and we get co2 to optimum levels within a two hour gap is this not detrimental to fish health? Let's face it with a kh of 4 and a high o2 levels during the night (no co2 running + 10x turnover/surface ripple) the pH could be 7.5 maybe higher with good o2 (lack of co2). The ph drops to 6.6 (or lower if we have hungry carpet plants like hc) in 2 hours. Is this not too severe a drop compared to the gradual drop we would get with less bubbles per minute and co2 on 24/7? I would imagine with less bubbles and 24/7 we would use more co2 as there would be more chance of losing some through water movement and a slower injection rate. This is more of a fish health question as I would think the plants would not care about the drop in pH and more interested in the carbon available.

 

[ian_m]

1. Fish don't care about minor pH changes, even less so if its over a period of hours. This occurs in nature, fish have evolved to cope.

2. Fish don't care about CO2 levels PROVIDED doesn't generally exceed 30ppm and there is O2 dissolved in the water. This occurs in nature, fish have evolved to cope.

So turn on CO2 to get levels for your plants when lights on and stop wasting gas at night and wasting worries over a non issue.

Oops significantly more than 30ppm CO2, are fish bothered, nope.

That's better...again are fish bothered...nope.

 

[dw1305]

Hi all,

Is this not too severe a drop compared to the gradual drop we would get with less bubbles.......

It is like "ian_m" says, the change in pH due to the addition of CO2 is different from a rapid change in pH caused by changes in water chemistry. We haven't changed the water chemistry, we've just changed the HCO3- ~ H2CO3 equilibrium. Once we stop adding CO2 the pH (measure of the extra H+ ions from H2CO3), will return to its equilibrium value. Certainly for soft water fish it is changes in water chemistry that effect them, not changes in pH.

From <"Question about pressurised...."> & <"Question about 1 pH unit drop..">

Calcium carbonate is insoluble in water, but in water with carbonates present the small amount of CO2 (that goes into solution as H2CO3) is in equilibrium with the HCO3- to give a stable value of ~pH8 at atmospheric CO2 levels (400ppm CO2) and standard barometric pressure (1013mb).

When we add CO2 above atmospheric levels we drive the H2CO3 ~ HCO3- equilibrium towards H2CO3. We know that pH is a ratio, and that an acid is defined as a H+ ion donor and we've added extra H+ (from H2CO3), so the pH falls. How much the pH falls depends upon the reserve of carbonate buffering, we usually measure this as "dKH".

This is more of a fish health question as I would think the plants would not care about the drop in pH and more interested in the carbon available.

I think this is a valid concern, and I'm not a CO2 user.

Soft water fish are adapted to rapid changes in pH (pH is a ratio, so as we approach pure H2O it becomes less and less meaningful). For fish from very hard water it may be different. In very heavily carbonate buffered systems (like Lake Tanganyika) fish are adapted to stable high pH, because it takes a huge changes in water chemistry to effect pH.

I don't keep hard-water fish, or use CO2, so I have no practical experience. Anecdotal evidence at least suggests that <"hard-water snails don't do well in CO2 injected tanks">, due to shell erosion during the period when the water is acidic.

cheers Darrel

 

[Antoni]

Hi guys,

Lately I use co2 24/7 and I feel the results are better. Better growth, less problems. To be honest, running co2 24/7 doesn't waste that much of a co2 compared to pumping it for 8-9-10h a day. Generally I use lower bubble count - around or lower the 1bps per second 24/7 compared to 2 bps per second for 9 or 10h a day in my 50l tank.