pH drop with CO2

[Waterloo Kid]

I've just started using a DIY CO2 setup. I have the CO2 diffusing through an air stone that is situated below the outlet to the filter. As the bubbles rise they get caught in the outflow and fired round the tank. The absorbtion is pretty thorough with only tiny bubbles making it to the surface.
I started this setup last night and initially the volume of CO2 was high. It's down to a trickle now. My pH has dropped overnight from approx 7.4 to 6.8 I do not know if it will drop any further. I will keep it monitored. My question is, is this drop to be expected or is it high? The setup is running off one 1.5 litre fermenting bottle at the moment and the tank is a Rio 400 (88 gallons). I'm surprised at the effectiveness of the system!
Also, if the plants don't pearl is that a sign that the lighting is too low and the CO2 injection is a waste of time or am I being super-impatient?

WK

 

[Silly me]

If the plants use the CO2 at any faster rate the PH wouldn't drop that much.. what is your current light setup?

 

[George Farmer]

Hi Waterloo Kid,

If your pH is 6.8 and KH 2 degrees (as stated in your signature) then your CO2 level will be approx 10 mg/l. This isn't a huge amount of co2, ideal is between 15 and 35 mg/l depending on your plant density and lighting. Also be aware that with a low KH of 2 you will have to keep an eye on your pH, especially if you intend to increase your co2 levels.

I experience pearling with 1.8 Watts per gallon and co2 at 20 mg/l, I find the faster growing plants pearl the most (makes sense).

 

[Waterloo Kid]

I tested the KH yesterday before application of the CO2 and it was in fact 4 degrees, not 2. Must update the sig!
My current lighting uses the standard (infamously underpowered) juwel light bar with two 40W 48" T8 tubes. One is an Aqua Glo and the other a Flora Glo. Both have reflectors. Since I am using reflectors does this effectively double the wattage of the bulb or just adda bit? If doubled then I am running at 1.8 wpg. If no then close to .9 wpg.

How's that for lighting?

WK

 

[George Farmer]

4 dH is better!! That's 21 mg/l co2 @ph 6.8

On your lighting; when using reflectors, true it almost doubles your light output, but I wouldn't apply that to the watts per gallon rule. So you have the 0.9 wpg.

I would also be aware that your tube choice may not be the most effective. I believe Hagen Aqua-Glo has a colour temp of 18000K and Flora-Glo 2800K. It has been suggested that the best colour temp for plant growth is between 5000K and 7000K. That said, many people have good results with higher and lower temps, myself included so it's up to you. My opinion is that most plants adapt to whatever colour temp, spectrum etc. and it's more the intensity that's important. If you are serious about growing a lot of plants, perhaps some of the more demanding, then you can add another Juwel light-bar or DIY some extra tubes as I have done in my Juwel Rio 125 (pictured below).

What plants are you growing or intend to grow? You could have an awesome tank with a Rio 400, I'm jealous

 

[Waterloo Kid]

Right now I'm trying to grow anything! I have some hygo. polysperma, amazon swords, pygmy chain sword, java moss, vallis, four leaf clover, anubias nana, anubias barteri and didiplus diandra.
The four leaf clover is throwing out new immerged leaves and the chain sword is showing signs of growth. The barteri has 1 new leaf. The Amazons are showing signs of brown leaf spots. They are in fresh sterile gravel but I have placed root tabs in there. I'll give them time.
I've heard that the Aqua Glo bulb, although marketed as 18,000K is actually nearer 7,000K.
I like the look of plants and so I might invest in a T5 unit (twin bulb) to cram under the hood with the existing. That should give me loads of light!

WK