Is 40ppm KH too low? - The Planted Tank Forum
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post #1 of 5 (permalink) Old 10-29-2003, 07:18 AM Thread Starter
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Hi guys, I,ve been reading posts here for awhile but I thought I would introduce myself and ask a question or two. I have a 170lt (35 gal) heavily planted tank with PH7 and KH 2.2dg or 40ppm. I,m supplementing CO2 with a carbo plus unit and add seachem fertilizer. Light is 1x36watt gro-lux, 1x36watt 10000k tropical aquastar and a 5000k 140watt compact fluro. Is the KH too low for good plant growth. Ammonia, nitrite and nitrates are all O. Nitrates go up slightly with a heavy fish feed. (45 inches of fish). I also have a question about eheim CO2 monitors. Mine went to yellow which is supposed to indicate too much CO2 but when I did a PH, KH chart comparison the chart said I only had 7 ppm of CO2. So which one is wrong, the eheim monitor or the chart. Thanks.
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post #2 of 5 (permalink) Old 10-29-2003, 01:48 PM
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Well, if your test kits are good, then I would be inclined to believe the chart indicating 7ppm. That sounds about right for the pH and KH you are posting. The relationship between pH and KH is pretty tight, so it's a pretty good indicator of your CO2 levels.

I have not had any experience, or heard from anyone who has used one of those CO2 indicators. I know that they have a reagent that must be added every now and then. I'm not sure on the accuracy of them. At what point does the indicator turn yellow to tell you that there is too much CO2?

Can you put the CO2 indicator in a bowl of tap water? That would tell you if the indicator was bad or not.
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post #3 of 5 (permalink) Old 10-29-2003, 03:10 PM
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can you tell me what part number is that co2 monitor? I could not find it in the Eheim site.

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post #4 of 5 (permalink) Old 10-31-2003, 02:02 AM Thread Starter
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Hi guys, DleDeaux I think you might be right 7ppm sounds more like it to me as well. I will do what you say though. I,ll compare readings tonight with some tap water. I,m not sure if the monitor is working properly. When I use the regent in 1ml of water the reading matches the chart but the actual monitor has a different color. Maybe I haven,t got it in the right place? Its about 6 inches down from the waters surface, does that sound right? Scorpion, the part number is 6060200. What about the KH guys, is it too low?
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post #5 of 5 (permalink) Old 10-31-2003, 03:23 AM
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It's not too low for growing plants. When I first set up my 29, I was running with 1.12 KH and I have been slowly increasing it using crushed coral in my filter. I have been adding 1 tablespoon every couple of weeks and I am up to 3.36. I might add one more tablespoon, though I am pretty happy with where I am at right now. I run about 6.6 to 6.7 pH which puts me right at 20 to 25ppm CO2.

Basically, what increasing your KH will do is allow you to put more CO2 into the tank before it starts to affect your pH. People with really high KH can have very high levels of CO2 with only a pH of 7. The lower your KH gets though, the lower your pH must be in order to have the same amount of CO2. This is really a bird's eye view of what goes on, but it should give you a starting point. Here is a link that gets into a little more detail and gives a nice chart that shows the relationship:

As for the CO2 indicator placement, I'm afraid I couldn't really say how it should be placed. I don't have any experience other than seeing them in catalogs. I am inclined to believe that it wouldn't matter too much where it was placed. I could be wrong though.
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