Hi all.
I have a 90 gal. low tech tank with 1.5 WPG shop light.
Recently I was wondering what would I expect to see if I injected co2 in this tank ,so I went for it last weekend and set it up with a power head mist.
I know Tom Barr mentioned that any FW tank will benefit from co2 injection,this tank is full of stem plants and a couple of Java ferns and Belleri swords ,I was adding Excell before but now stopped and it's only co2 ,no ferts ,about 40 small fish.
So I guess I am asking :what should I expect to see in terms of plant growth?with less than 2 WPG will I see faster growth ? should I increase the light period from 9HRS to 11HRS ?
Any input will be appreciated.
Ken.

When you add CO2 in a CO2 limited tank, you raise the need for uptake of nutrients which tend to be 5-10x higher. You would need to raise the amount of nutrient dosing and do the standard EI method w/water changes except the dosing frequency is the same due to low light.

Regards
Peter Gwee

I think that tank is light limited, not CO2 limited. He would see some improved growth, but probably not enough to require more dosing.

I don't think EI would be appropriate in that kind of tank, but I'll leave that to the EI experts.


Bill

In a couple of weeks you can tell us what you experienced, then we will all know how to answer that question if it comes up again. My gut feeling is that you will need to do some small dosing, maybe once a week, of nitrates, phosphates and traces, but I agree with Bill too, that the tank will still be light limited. (Actually, I think all of them are.)

Excel will help about 50% less than CO2 for this light level.
You should do pretty well.
Give it a week etc, but add ferts etc(2x a week at about 1/2 EI levels).

Plan on doing water changes.

Regards
Tom Barr

In a thread on the "Walstadt Method" Tom said, in part:


From that and other posts I assumed that water changes in low light tanks, with or without CO2 injection, should be avoided, mainly because of the danger of introducing excessive nutrients, such as ammonia, with the new water and causing algae outbreaks.

But in this thread Tom said,


So obviously I am confused, not a rare state for me. EI does require water changing, of course, but in a light-limited tank such as the one under discussion is the plant growth going to be robust enough to require that much dosing?

Thanks.

Bill
Thanks.

Bill

Well, it never wasa true non CO2 method to start with

Excel and CO2 are not non CO2/Carbon enrichment methods.

No reason you cannot gain the beneiots with eI at low light, just do not need nearly that much dosing and in many cases, fish waste alone can add "enough", but you can still top off to be sure with light EI. It does no harm. Some enjoy scaring others that it might, but this is due to a lack of experience and other issues they have, not EI by itself.

I have used EI at 1 w/gal and at 1.5 w/gal for several years without any issues w high fish loading and with no fish load. Hard and soft water etc.

It was VERY EASY.

Now you may get away with less dosing and less water changes, there is much more wiggle room with less light in ANY and EVERY dosing routine for very obvious reasons.

But that is a matter of tweaking to your own taste for a routine(Say: I'm lazy and want to do 25% water changes once every 2 weeks instead).

But the 50% weekly still works super and makes things more stable in general if you add good CO2, Excel etc.

When I discuss non CO2, it does not imply Excel dosed tanks.

Nor does Diana nor anyone for that matter I know of.......
Yea, it's not CO2, but it is carbon enrichment........

Regards,
Tom Barr

Bill, the reason to avoid big water changes when you are doing a no-CO2 tank is to avoid introducing CO2 with the water change, not other nutrients. Tap water usually has some CO2 dissolved in it, so adding half a tank of tap water adds considerable CO2. Then the CO2 dissipates and is used by the plants, bringing the tank back to under 3 ppm of CO2. Those peaks of CO2 followed by very low CO2 can trigger algae blooms.

Please excuse my continuing confusion, but if you do EI with its 1/3 to 1/2 tank volume water change, aren't you causing the same CO2 spike and drop that could cause algae? Even with the injected CO2, these plants aren't going to need much in the way of nutrients with 1.5 WPG, particulary if they are low light, slow growing plants like crypts and anubias.

As Tom said, "Walstad-type" tanks shouldn't have have many water changes (for the reason you stated) and it would seem that would also extend to all low light tanks, even though they used injected CO2. Right?

But then Tom also said that he has kept low light tanks with and without CO2 injection and used EI without problems. So then maybe the warning not to make large water changes in "Walstad-type" tanks can safely be disregarded?

If that's true then I'm no longer confused, at least until the hard core Walstad-ites begin their rebuttals.

Bill

It has nothing to do with EI. If you dose CO2 the additions of CO2 due to water changes are not significant. If you don't dose CO2 the CO2 additions due to water changes cause a fluctuating amount of CO2 in the water, leading to algae. If you want to fertilize by the EI method for a no CO2 tank, first the doses have to be much smaller, since the plants don't grow very fast, and don't need the additional fertilizers. Then, any water changes have to be few and far between, which isn't a problem because you are dosing so little of any fertilizer anyway.