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Re: ISFET Ph pens and controllers

> Date: Wed, 16 Aug 2000 21:47:28 -0400 (EDT)
> From: dirk_matthys at technologist_com
> <Dirk unhappy story snipped>
> Currently I inject  Co2 continuously. But in December I will move from ADA 
> country back to Belgium. As you can imagine, a project is in the planning     
> stage. 

A near-Dutch tank, no doubt ;-)

> I have always been fascinated by the Ph controlled Co2 systems.
> But know I am getting my doubts: The buffering capacity of the water changes  
> along with water changes, leaching of driftwood, use of humic acid containing  
> substrate etc…. 

Those are controllable by you. Driftwood and substrate are your choice. Doesn't 
Dennerle in Germany sell ceramic "driftwood"?  Use plain gravel substrates with 
laterite. If you have soft (low KH) water, add sodium bicarbonate at water 
changes; we do. If you have higher KH water, mix with distilled or RO water or 
accept a higher pH.  

> So the Co2 input of such a system is far from stable. Imagine your Ph goes     
> below 7 without C02 (ADA soils do that). How can the controller add Co2?       
> Increase hardness??? 

It can't. I guess I wouldn't use ADA soils.
> The probes need to be adjusted continuously, and the spare parts are expensive 
> and may not always be available. I am really starting to wonder if it is worth 
> the investment.

We think they are even with the annoyances I mentioned in an earlier post. All 
three tanks have them. 

> I can also build a continuous pressure/ flow system that I adjust by measuring 
> Ph chemically.  Does it make such a difference if a controller regulates your 
> system? Is it going to make a significant difference in plant growth? 

No on both counts. If you diligently monitor what is going on, a constant flow 
system is fine. We did this for years in a low tech tank with an UGF plus an 
Eheim canister filter. We fed CO2 into the Eheim filter instead of a reactor. It 
worked just fine but it took some fiddling. And sometimes we weren't as diligent 
as we should have been.  

> How many ways of measuring Ph electronically are there anyway? 

I'm clueless. "6"?

> Are professional probes more reliable/usable or worth the expense? 

Not in my opinion. Actually, as far as I can tell, there is no such thing as a 
"hobbyist" probe - all of them are "professional". The only difference is the 
application for which they are designed. 

> Are there any ISFET based PH controllers for aquarium use?
> Can ISFET based probes resist continuous submerging? 

I don't know; this is the first I've heard of them. But I bet "spare parts" 
would be easier to find for a "regular old electrode" controllers. 

George Booth in Ft. Collins, Colorado (booth at frii_com)