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pH fluctuations? GH drift?
hi Alex,
very bright halogen light), and when in doubt, I always create the control specimen, which is measuring the pH of my tap which is really high in pH. there is a marked color darkness difference between very high pH (using tap water), which does reflect the 7.6 color on the chart. but what i get is The most likely reason that your tap water has a high pH is that it's low in CO2. The CO2 level of the water straight from your tap might be variable at different times. That's why such a reference sample is unreliable. You should let a cup of water sit for a while, or aerate it, before taking its pH. At KH of 2 degrees, your pH at equilibrium should be about 7.2. That applies to both tank water and tap water. the tap when left out for over 24 hours, the pH reads about 7.8... we think the municipal water department adds something to make the pH artificially high... the tank pH is lower than the tap (even after left out for several days). probably because of the fish and the bog wood and stuff... good to know KH=2 stabilizes at around 7.2... How wide can the plant-respiration-induced pH fluctuation be? can it really go from 7.0 to 7.6? (37G, moderately planted...) It sounds like you have plenty of agitation. But if there wasn't enough, the plants could easily bring the pH up to 7.6. That only equals a 2 ppm drop in CO2 from equilibrium. Of course, the plants would consume more CO2 with higher lighting. How much light do you have? Any sunlight entering the tank? it has one 55W CF through a glass hood and is on about 12 hrs (11am to 11pm.. so there is about 5 hours of "not pitch dark" ambient, filtered, indirect light into the room prior to the lamp going on). so the tank is about 1WPG (assuming about 30% loss in light intensity through the glass). the tank is in a well-lit room with lots of windows, but the tank itself is about 8ft from the closest window. it used to get a short direct light just before sundown, but right now I have the drapes so it doesn't get any direct sunlight (my feeble attempt to control algae..) for the past few weeks. the room is still quite bright though (lots of windows). As I said, it seems like there is more than enough agitation from those 3 sources. :-) fun watching danios surfing the current.. whhhheeee!!! no. GH went *up* from 2 to 6... and no.. I have no rocks or any Okay, I misread that part. It might be due to snails dying and their shells melting, but I'm not as certain about that. Or it might be the way you're reading the GH kit results. I have a hard time with my AP GH test kit. The color change from greenish-yellow to green is too subtle. Sometimes I miss it and keep adding drops of the test solution. yeah. I used to have that problem until now I look at the color by looking directly into the tube from above.. This seems to give me better color distinction just at the titration point. usually after two drops, the yellow/orange is so faint, I can't tell when it turns green.. but these days, more drops I put in, more yellow/orange it gets (and I shake the tube using the cap too...).. so there is no mistake that GH is much higher than it was before... it's just.. strange... Anyway, I think a large water change would greatly help reset the water parameters, and balance things out. Change perhaps 50% of the water, and see if the GH, KH, or pH start to drift again. Make sure you take the pH ok.. this weekend is my maintenance weekend, so i'll do larger water change than usual (usual is about 25%) readings at the same time each day. Then test the water at different times on a single day to see if there are any daily cycles. good point. I usually test in the evenings (after I get back from work). I'll try a few days in a row, at the same time, and over the weekend, I'll try morning, midday, evening test to see if I see anything.. wouldn't adding baking soda increase the pH of the water? if the water is already at or close to 7.6, I don't think it's such a good idea to increase pH further (esp for the fish)... are there other means to increase KH without increasing pH? Yes, more KH will increase the pH, but if the water is at 7.6, it's for some other odd reason. If the KH is 3, for example, the equilibrium pH at that level should only be about 7.4. But find out exactly why it's 7.6 before adding the baking soda. A way to increase the KH without affecting the pH is of course to inject CO2. The addition of CO2 can offset the pH increase due to higher KH. We currently think that the water dept adds something to make the pH artificially high for the low KH value (prevents corrosion? may be it keeps copper from leeching toxins or something? I don't know). I don't know what they add to increase the pH. when I test, ammonia, nitrite and nitrate is zero in the tap... I don't have any phosphate test kit or any other indicator to figure out waht they do.. may be I should ask. linda |
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