Re: wet drys

[Thomas Barr <tcbiii at earthlink_net>]

> Just wanting to see some other opinions out there, but I have always
> thought that wet/dry filters, trickle filters and even to some extent
> overflow systems with pre-filters weren't necessarily a good thing for
> plant tanks due to the fact that they're more likely to drive out CO2
> from the water?

Here are some possible causes for the myth surrounding this.

Overflow and prefilter systems that have a lot of splash and/or tanks with a
great deal of surface turbulence lose a good deal of CO2, but if these
sources of loss are addressed, a simple biotower does not impact the CO2
levels.
I use no more CO2 with such a filter than without.
.....do the test your self if you doubt things and see.
A lot of planted aquaria is not researched or addressed well and myths come
about and get duplicated again and again.
After awhile everyone believe them.

Another thing is the flow pattern. The water at the surface where an notched
overflow is placed takes in water that has the lowest amount of CO2
possible(this occurs at the surface) if you enrich tanks with CO2.

Most people that have sumps inject the CO2 there and the return water is
sprayed downward into the plants and towards the bottom of the tank, the
water then slowly rises up through the plants, to the surface and goes back
down for another cycle.
 
> CO2 is not highly soluble in water on its own, and is readily driven out
> - - more so even than oxygen is due to its larger molecular size (larger
> than H2O molecules as well as O2 molecules).

You can literally see a CO2 bubble shrink then disappear as it goes up in
the water column. Seems pretty soluble to me. Not sure what you mean by
"not highly soluble in water on its own".

The diffusiveness of an unsaturated or a saturated gas is 10, 000 times less
in water than in air. That goes for O2 as well, both gases are generally in
excess in a plant aquarium all the time. O2 might dip down below saturation
for a few hours in the early part of the day/very late night. CO2 is always
outgassing from the surface unless a non CO2 enriched plant tank during the
photoperiod has been going for about an hour sometimes a little longer and
for a few hours after the lights are off.

Suppose the plants become limited due to a lack of some critical nutrient,
say NO3, and then photosynthesis declines say by 70%, what is going to
happen to your O2 levels then if you have a canister?
What will happen if you have a wet dry?
Suppose there is a large flux of NH4 after a pruning, or removal of a sword
plant that got too big?
The wet/dry or good sized canister filter will handle it, but wet/drys
really are the best NO3 producer on the block.
Better to have bacteria than algae. They do make a relatively good back up
should the plants become stunted or too much disturbance is done to them.
NH4 really has proven to cause a number of algae blooms.
NO3, PO4, etc when CO2 is being used does not have nearly the same intense
effect.
  
> As a general rule of thumb from where I come from out here (on the
> Australian East Coast), most aquarists here that I have talked to,
> including many FS's are anti-trickle/wetdry filters on planted tanks for
> this reason, and promote canisters, and to some extent hang-on filters
> (though some even do not agree with these as they believe these can also
> contribute to CO2 defficiencies).

Sounds like you folks need better CO2 diffusing methods:-)
Some filter blame is certainly true but these are based on surface
turbulence, splashing in the overflow etc.
I have been able to find/pinpoint the sources of most of these so called
losses. 

Simply parroting something someone else says, does not get it for me.
Folks said that negative things about PO4, RFUG's, lots of traces etc.
I am hard headed and needed to find these things out for myself.
Yes, I barked up more than one wrong tree but I got lucky on many issues.
Piece by piece I got things together.

> If these filters do drive out the CO2, then maybe the compressed CO2
> system or DIY yeast or whatever is being used, may be operating in
> adverse conditions...

Naw. It can be the case(see above and below) but more likely:
Either the:
The filter is not set up well(too much splash and surface turb
The CO2 system is not set up well(not enough flow through/water
passage/circulation relative to the tank size, reactor that waste the CO2,
system has a leak, improper seal etc)
Poor flow pattern in the tank.

> Or maybe there is a point where the individual has
> to weigh up whether they want to spend a lot of money on huge canister
> filtration, and additional biological filtration systems (maybe
> fluidized bed or something to bring the filtration up to the same
> standard of the much cheaper (for large systems especially) and highly
> efficient wet/dry system and just 'bite the bullet' when it comes to
> having to replace the lost CO2?

Oh! The painful cost of CO2, have you seen the prices today?
12$ for 10lb tank refill that last a year for a 160 gallons worth of tank.
Even if I lost 1/2 of the tank, that's 50 cents a month.

> Then again, here where I am, compressed
> CO2 systems are very expensive for some reason - my main supplier sells
> Dave Gomberg's system for $285.00AUS.. If you want self-controlling
> stuff then you're looking at $550.00AUS minimum and you still have to
> add your own celenoid and pressure regulators etc! And that's the
> cheapest supplier too... Plus finding a local welding supplier which has
> all the fittings and necessary precision valves here is like attempting
> to push a mach truck up a hill. So I guess we're more conservative when
> it comes to pressurized CO2 addition :)

There's that but a better flow pattern, better CO2 diffusion/reactors, a
little surface turbulence is okay, just not a lot, reducing the splash in
the overflows will go a long way to solving any CO2 issues.

But the issue of the cost of gas system vs the prices here in the US have
nothing to do with the cost of the gas itself.........
What does a refill for a 5 or 10 kg tank cost?
And if you figure out a good way to diffuse the CO2, DIY can be effective as
well, but requires constant weekly upkeep for the brew or modifications to
the brew mix etc.

> and some forms of Hygophila spp. I'd love to know ideas on the wet/dry
> stuff as it would be much more beneficial for my beloved discus to have
> the luxury of the wet/dry filter! At the moment I'm looking at fluidized
> bed filters for biological -

I'd stay away from FBF's. They crash pretty fast if not constantly
running(15-30 minutes down time will do this apparently).
I would not set up a Discus tank without a wet/dry personally.
Regards, 
Tom Barr 
 
> Any ideas out there?
> 
> Cheers,
> Adam Shaw