Has anyone tried the diy system in the articles section?
Thinking of doing it as it seems to be safe enough. I've juwel vision 260, so can I just add another bottle of mix?Plants growing well at moment, just have one or two that could do with a boost. Would also welcome the effect of lowering the pH...have tried everything for that...pH lowering solutions didnt work... got fresh bogoak and cleaned and sterilized it... a month or more after its introduction and it still hasn't lowered it.(pH at nearly 8, sometimes at 8...ideally would be better about 7. Have check that all my materials in tank are not effecting it... all are inert stone and acidy bog oak...pH in tap is usually 7, but is hard-very hard I reckon, tis well water and leaves plenty of limescale in the kettle.also thinking of maybe getting RO unit in next month or two, for this problem)

What about the Co2 and the fish? Is any surface movement going to do away with the Co2 you put in? Will there be enough O2 for fish?or is it a matter of just watching carefully to figure it out?

So sorry this has taken me ages to get back to you.
Ive just been so busy at work and home lately that everything else has fallen by the wayside. Sorry.

To try to answer some of your questions:
- I run my DIY setup on a Juwel Vision 180 (with internal filter removed and using an external Eheim 2126 instead) so yeah, to get the extra CO2 you want, I think you could add one more 3L bottle should do the trick

- as Im sure you know, adding CO2 will lower pH so perhaps as you are already going to be adding more CO2 then your problem about the pH will also be solved?

- surface movement is claimed to drive off CO2 by increasing the surface area of the water (most people believe that even a gentle ripple across the surface wastes CO2). However, I run my return pipe from the Eheim filter close to the surface and pointing slightly at it to give me quite a current in the tank and a good surface movement.
Two reasons for this:
1) the surface of the water is broken, so eliminating any oily film that accumulates from food and other stuff which is bad for fish health
2) the good current in the tank helps keep down algae and prevents "dead" spots of low oxygen/CO2

- I would suggest you get a "drop checker" to test for CO2. As you rightly say, too much CO2 can badly affect your fish; yet for optimum plant growth you want CO2 around 30ppm so its a balancing act making sure you dont harm anything.
A drop checker will give you a permanent in-tank test which in my short experience using it, is very reliable and accurate (if sometimes a little difficult to read).

P.S. you mention that your water is quite hard (which is exactly like mine),. Thats not the best for plants, so choose carefully, but there are some stunners that Ive really enjoyed and have come up great in the harder water.
My fav at the moment is MONOSELENIUM which loves calcium so its going to do great in your harder water. This coupled with the fact that it doesnt like alot of light, and has a natural algaecide in it, my amano shrimp like pruning it, my male gourmai rips pieces off for his bubble nest, AND its a lovely dark green carpeting plant, means it really can look stunning.

Hope this helps

If you need anything else at all, especially when it comes to putting together the CO2 system, please ask.