Another DIY CO2 question

[Kim&Dan]

Hey guys!

I've built two DIY CO2 reactors as suggested in various other threads last night. They started working just after a couple of hours yesterday and today they were bubbling away pretty nicely.

The main reason I did this wasn't actually to speed up plant growth (as they are developing pretty well anyway) but to lower the PH of the water avoiding the powder additive/peat options.

As we live in Dunedin the water that comes out of the tap is very alkalic 7.2-7.4 PH and quite soft - I think someone mentioned it in another thread to be somewhere around 2 KH. We aren't actually using water straight from the tap but water from the Speights brewery, which at least doesn't contain chlorine. The PH is still over 7 though.

Now, after 24 hours of CO2 injection the PH dropped to 6.6! I stopped the CO2 injection right away as this drastic change surely isn't good for the fish (even though none of them show any signs of stress or the like). I have put the airstones back in there pumping regular air into the tank. :-?

The mix I used was in a 2l bottle: 3/4 warm water + 2 cups sugar + 1 tsp yeast + 1 tsp baking soda. The diffuser used is just a regular airstone hanging half way in the tank - most of the CO2 shouldn't even dissolve in the water this way :-?

Or does it dissolve itself by sitting on the surface of the water (being heavier than air)? Is this dangerous for the fish, especially for the gourami? How come the PH dropped by this much? Does it have something to do with the water being so soft - ie there is not enough 'buffering' going on?

BTW the tanks are both 2 feet in length - stocked with Guppies, Platies, Cardinal Tetras, Kuhli Loaches, Yoyo Loaches, Bristlenoses, Dwarf Neon Rainbowfish, Three-Striped Gourami.

Any ideas of how to get this working properly? Could I run the CO2 reactor AND the airpump simultaneously to balance it out?

My aim would be to have the PH somewhere between 6.8 and 7 ideally. 6.6 should be good for the Cardinals and the Yoyos but the best compromise to make them all happy is 6.8

Looking forward to your thoughts!

[Luke*]

Hi there Kim&Dan, the ideal KH (carbonate hardness, not general hardness or GH) is 6 for buffering capacity. Due to your low hardness you are correct that is most likely why the pH dropped so suddenly.

You used a lot of yeast, try 1/4 or 1/2 teaspoon, this will also make your mix last longer. Your sugar quantity is ideal. Forget the baking soda, wives tale. Add it to your tank instead, 1/8 teaspoon, this will bring your buffer capacity up and pH with it. You will learn how much baking soda to add compared to CO2 over time.

The airstone isn't very efficient yes, but a lot of CO2 is still diffusing into the water as the bubbles rise. No, the bubbles don't sit on the water they pop and disperse into the air.

Assuming you have 2 tanks, sounds like quite well stocked, so the wastes of the fish bring the pH down too. You said the pH out of the tap is 7.2-7.4 but have you tested the pH in the tank a while after a water change? How often do you water change? It will gradually drop in soft water.

HTH

[Kim&Dan]

Thanks for that, Luke!

You used a lot of yeast, try 1/4 or 1/2 teaspoon, this will also make your mix last longer. ... the baking soda, wives tale. Add it to your tank instead, 1/8 teaspoon, this will bring your buffer capacity up and pH with it.

I'll try using less yeast then! Are you sure about adding a bit of baking soda to the tank? Is this safe considering the fact that the PH is fairly high already? Bringing the buffer capacity up would definitely be good but what about the PH?

No, the bubbles don't sit on the water they pop and disperse into the air.

Ok, that's good news as I read somewhere that the CO2 is heavier than air and would sit on top of the water

Assuming you have 2 tanks, sounds like quite well stocked, so the wastes of the fish bring the pH down too. You said the pH out of the tap is 7.2-7.4 but have you tested the pH in the tank a while after a water change? How often do you water change? It will gradually drop in soft water.

Yes, the two reactors are for 2 2feet tanks and they are well stocked but not overstocked. I've noticed the PH going down after a few days - usually from 7.2 to 7.0 in about 10 days. We change 20-30% of the water weekly by hoovering the gravel.

Thank you for your advice! Really helpful as always

[DubbieBoy]

Hi Guys,

As Luke says, use less yeast and the mix will last much longer. As yeast ferments the sugar, there is a gradual buildup of ethanol which is toxic to the organisms themselves and kills them off. After your mix has been brewing for a couple of days, take a big sniff and you'll see what I mean By adding less yeast, you'll slow this down a lot but still get plenty of gas.

As the Dunedin water is sooo soft (which is good for your washing machine and for your kettle!), it has no buffering capacity to speak of, which is why the pH of your tank water is liable to change quite quickly even with a small amount of CO2. The best way to get around this is to add sodium bicarbonate (baking soda, NOT baking powder which is different!). There's a rule of thumb that 1 tspn, or about 6g, should raise the KH of 50 litres by 4dKH. As with all things, do it slowly. I would aim for a KH of between 4 and 6 degrees (there are good test kits available at Pet Warehouse and at Pet Planet).

Having said that, however, my own advice would be not to bother interfering with the pH at all. In smaller tanks, particularly with low KH, it can be hard to control pH via CO2 injection, even with pressurised systems. With a DIY setup, its even harder. But then, I don't really believe the fish care all that much as long as the pH is reasonable and stable. We probably do more harm than good a lot of the time when we try and control these things, especially in smaller tanks.

You've got two DIY CO2 producers going - so grow lots of plants!! If you're not so interested in the plants but moreso the fish, there are probably better ways of decreasing your pH than with CO2.

[Kim&Dan]

Hey Rory!

Thanks for your advice!

I think you're right and I'll just leave the PH where it is for now. It's just that in the LFS they kept telling me that our PH is too high, even though the fish don't really seem to mind... :-?

Thinking of the plants on the other hand... I have a little tap for airpump tubes - I was wondering, if I were to add it to the CO2 reactor and just keep the CO2 injection at a really low rate - would that be any good?

[DubbieBoy]

I really wouldn't recommend restricting the output from a DIY CO2 generator - they can actually build up a LOT of pressure, to the extent that the bottle may explode (very messy and smelly too ) Equally, small plastic airpump valves can't control the pressure either.

Maybe the best may to limit the amount of gas produced is just to limit the amount of yeast, you'll get less gas and your mix will last longer. Or keep it somewhere cool.

A pH of 7.2-7.4 is really not particularly high.

Have fun!!

[Warren]

7.2-7.4 is not high at all. When you consider the pH scale is logarithmic it further shows how 7.2-7.4 is nothing to worry about. If it was 8 or more then it may be worth worrying about.

Fish are usually very adaptable. If they look happy they usually are. I wouldn't muck with the setup. If it's stable, you only risk disaster by mucking with it...

[Kim&Dan]

Thanks for your thoughts!

A pH of 7.2-7.4 is really not particularly high.

7.2-7.4 is not high at all.

That's what I thought but not being 100% sure I took the advice from the LFS... a lot less to worry about then now