CO2 Diffusion

Discussion in 'Carbon Dioxide (CO2)' started by REDSTEVEO, 27 Apr 2008.

  1. REDSTEVEO

    REDSTEVEO Member

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    Hi guys,

    Here is my problem, I hope you or someone you know may be able to help. The problem is despite getting what I think is everything right as per the reccomendations and the plants grow healthily (heavily planted with hair grass and riccia at the front, tiger lillies and large leaf plants at the back with mosses on bogwood in the centre) I don't see massive amounts of photosynthesis. I have a very low fish level, 6 x Otticinclus, 4 x flying fox, 6x rainbow tetras.

    My tank is a trigon 190 filtered by an Eheim Professional 2 external canister filter. The return water is spread via 2 spray bars at 90 degrees keeping a good flow of water moving throughout the tank without too much turbulence. Temperature around 26 degrees. My CO2 system runs off a 2Kg bottle with a PH sensitive electrode. When the PH goes up and reaches 6.8 the CO2 switches on and stays on until the PH reaches 6.5 and then switches off. It usually takes anywhere between 10 minutes and 30 minutes for it to switch off depending on the time of day and how many lights are on. This runs 24/7. The bottle lasts around 4 months. The CO2 goes through the bubble counter at the rate of 1 per second. I can increase the number of bubbles but this just drops the ph quicker and does not necessarily put more CO2 in. I have a permanent CO2 colour indicator inside the tank which shows a lime green to yellow colour indicating that the CO2 is at the right levels.

    The diffuser is the JBL Spiral type where the bubbles slowly spiral around mixing with water on their way up. I used to use a water driven diffuser from DUPLA but that needed a water supply off the main outlet pipe and looked a bit messy. The JBL one has a gas escape tube at the top and I noticed that CO2 would escape through that and straight to the surface when it built up at the top of the diffuser. I though that this was a waste of CO2 so I have connected a small length of tubing to it and ran it to one of the spray bars where I thought it would get sucked along and pumped through the tank. Instead a small column of water from the spray bar goes back into the diffuser and no more gas is escaping so I gues that this is an improvement.


    I don't do 50% water changes every week. I use RO water and change 30 litres once a fortnight. I add 20 mls of liquid KH buffer, 10 mls of liquid iron and a flat teaspoon of Sera Mineral salts at each water change.

    The lights all have reflectors and are all on timers coming on gradually until they are all on around mid day. There are two 24 inch 30 watt Sera tubes in the centre, a smaller 20 watt tube at the back and a 30 watt T5 tube at the front. At the peak all lights are on for around 2 hours at midday and then go off towards the evening. The smallest light comes on at 7:30 am and goes off at 8pm at night.

    The KH is 4, GH 10. If the PH does not go up the CO2 does not come on. I add KH buffer, the PH goes up and the CO2 comes on. It all seems to work well and I don't have any problem with ammonia or algae, I just don't see the photosynthesis I expect and wondered why.

    What do think is the problem?

    Any help appreciated.

    Thanks,

    Steve.
     
  2. Ed Seeley

    Ed Seeley Member

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    The first thing I'd say is that your pH meter is causing you to have inconsistent CO2 levels. This will cause you far more problems than any percieved issues with the pH. I run my tanks with pure RO water (remineralised with powders) and simply run my CO2 at 30ppm. This causes a pH swing of 1 degree when it comes on in the morning and off at night. The fish are uneffected by this. Without stable, high levels of CO2 the plants photosynthesis cannot run at high levels.

    If you want to use your pH controller then use it as a safety device only so that it will cut the CO2 off if the level drops too far. For day-to-day use get a drop checker with 4dKH water in it and set the bubble rate of the CO2 so that this stays green. If your water's normal pH is about 6.8 then I'd set the safety level for your pH meter at about 1 degree below that so 5.8 or you could just turn it off and simply run the solenoid on a timer which is how I run CO2 on all my tanks.

    On a side note, you say you don't see massive amounts of photosynthesis. How do you know? Do you mean the plants don't pearl after a while? This can be down to a number of issues including not enough CO2 or not enough fertilisers.
     
  3. Ed Seeley

    Ed Seeley Member

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    Forgot to say, I also found that the JBL diffuser was not terribly efficient and switched to a CO2 reactor or glass diffusers to produce microbubbles. These give really good results and can simply replace your JBL 'ladder'.
     
  4. REDSTEVEO

    REDSTEVEO Member

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    Re: CO2 Confusion?

    Thanks Ed,

    I will reset the PH sensor to 5.8 like you have suggested. I seem to remember the last time that I did this it was almost permanently on trying to bring the PH down so that the sensor would switch off. That was because I had discus in the tank and not as many plants. I will let you know how I get on.

    If it is not the CO2 which is causing the lack of photosynthesis what other nutrients do you reccomend other than liquid iron and what dosage would you recommend?

    Thanks again for your swift reply.

    Regards,

    Steve.
     
  5. Ed Seeley

    Ed Seeley Member

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    Re: CO2 Confusion?

    No worries. Before you adjust the pH meter make sure that you set the bubbler rate so that it cannot add more than 30ppm CO2. You want to control the amount of CO2 by the bubble rate and then the solenoid is there purely as a safety cut out, not controlling the CO2 level.

    Almost everyone here adds Potassium Nitrate, Potassium Phosphate, and Trace Elements. Once you get light levels up higher you need to give the plants some macro fertilisation to feed the plants. Look at the EI article on the fertiliser section (http://www.ukaps.org/forum/viewtopic.php?f=11&t=13) and Clive's article in the Tutorials section (http://www.ukaps.org/forum/viewtopic.php?f=34&t=1211).

    Basically you add these fertilisers daily or every other day to the water and then do a large water change every week. Personally I run a leaner system but use a nutrient rich substrate to make up for the days when I forget to dose...

    If you want a simpler method (but more expensive) then Tropica Plant Nutrition plus adds everything you need in one simple dose. George has used this with pretty great success!!!
     
  6. REDSTEVEO

    REDSTEVEO Member

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    Thanks again Ed,

    I know this must sound a little thick, but just exactly how do you tell that the water has 30ppm or that the bubble counter rate is set so that not more than 30ppm is going in. Do you mean set it so that there is not a massive amount going in very quickly and rather going in slower but sustained over a longer period of time?

    Cheers,

    Steve
     
  7. Ed Seeley

    Ed Seeley Member

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    You need to use a drop checker with 4dKH water in it to get a reliable measurement of the CO2 level in the water. You then start off at about 1 bubble per second through the bubble counter and adjust it slowly upwards to get a nice green colour in the drop checker. Adjust by tiny amounts and leave for a few hours as the drop checker takes an hour or so to catch up due to the slow rate of dissusion.

    I do indeed mean adjust it so that it's going in slowly over a long time, but by using the drop checker and carefully adjusting you will slowly add up to 30ppm CO2 accurately and the pH meter will just be in case of some emergency.
     
  8. REDSTEVEO

    REDSTEVEO Member

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    Brilliant,

    Thanks Ed I will keep you posted on the outcome.

    Regards,
     
  9. Aeropars

    Aeropars Member

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    I can also vouch that the JBL reactor is massivly inefficient. Thats the first thing I got rid of on mine as I was getting through loads of CO2. For your sized tank I'd recommend spending a few quid on an inline reactor. Now I've cleaned mine i can see just how efficient they really are!
     
  10. REDSTEVEO

    REDSTEVEO Member

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    Is an inline reactor outside of the aquarium i.e. in the line between the gas cylinder and the tank or what?

    Cheers.

    Steve.
     
  11. Aeropars

    Aeropars Member

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    Its attached to the outlet of your external filter.

    Its a chamber where CO2 is injected against the flow of the water and is battered about against mesh or other drtractors causing the co2 to be better absorbed into the water.
     

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