Corys and pH
 

So I tested my tanks the other day. My oldest tank dropped in pH big time(over time not suddenly) to 6.0 the lowest on the card. Also my tap has 0 KH so it can jump around. I read online crushed coral would work. In 3 of my tanks I just sat a filter bag half full with some of it. In the 12 gallon (pandas and pygmys) I laid it in the filter. Well that tank had the biggest change in a very short time period. The others went up just a little but the KH didnt budge much at all.

My pH reading yesterday was 6.0 with a KH of 0 ppm. Today its 7.2 with a KH of 20 ppm.
I am just worried bout how such a big change so fast will affect them,especially the pygmys as I know they are quite sensitive. Should I cut whats in the bag by half or just keep an eye on it? Should I do a WC? BTW my tap is 7.2 pH.

Thanks

Yes ,I would reduce the amount by half. I have not needed to use coral in some time but found that 1/2 cup to one cup per twenty gal to work for me.Smaller tanks than twenty gal would need less.

Okay thanks. I am about to test the tank again. Do you think my corys will be okay though? They seem fine,swimming around like normal.

Can't say ,all fish react differently to changes in water chemistry.Need to be careful when using things that change the chemistry. With Gh and Kh so low,,coral will work more quickly than it would in water that had some buffering capabilities and should be used a little at a time for this reason.

I agree with 1077, such rapid (relatively) fluctuation is serious, but what is done is done.

Any other fish in the cory tank? Were there pencilfish in there, the diptail Nannostomus eques if memory serves me--unless I'm thinking of another member? If this is true, the lower pH will not bother them at all. My 90g has these two species and many others, it is pH 5 or maybe less. But, steadying it with coral is not a bad idea. If you could keep the pH at 6 it would be perfect.

I can explain this further if you ask. I've a lot of experience with this issue, my tap water is zero hardness and I buffer my 115g with dolomite but I don't touch the other two currently.

Byron.