I have had my 40gal cichlid tank going for about 5 months. I posted here a few months ago regarding my terribly slow cycle that took 3 months to finish.
It has been a month now since the cycle completed. My ammonia and nitrite levels are always at zero

My question is this:

Is it normal/good that my NITRATE level is constantly at zero? I have only done one 20% water change in the past month, and the level is still zero. Even though the level was zero, I felt it was a good idea to give them a little new water. I thought that in the past few weeks there should have been at least some nitrate accumulation.

I use the API master test kit. The kit is 6 months old, and not expired. I have thoroughly shaken the bottles too. I know the nitrate test is valid because I have had readable nitrate levels in the past during the cycle.

I have a bit of reddish algae on the top of my large slate rock centerpiece that has been there for a few weeks. Could the algae be "eating" the nitrate? This is the only explanation I can come up with. Would it be reasonable for this bit of algae to be capable of consuming the Nitrate?

Any insight would be appreciated. Any comments on how to eliminate the algae would be great too! Thanks everybody!

Algae is a plant like any other, but unless you have a lot of it I doubt it makes that much of an impact. Would you believe kits read different from one to another?

How has your ph been doing? Tanks that sit for a while without fairlly regular water changes will tend to rise in ph due to the amount of dissolved solids in the water. Yours will start to creep up and believe it is inevitable without freshwater.

My pH level was 7.6 a month ago and it is currently at 7.8 according to tonight's test. I am going to do 20% water changes every couple weeks regardless. I would estimate that the slate surface is about 4" wide and 24" long. That gives me about 96 square inches of algae. There is a little algae on the fake plants too. My 5 cichlids are 2-3" long, so the bio-load isn't very large.

If I look really long and hard at the test tube, I think I can convince myself that there is a tiny bit of orange, so maybe the level is 0-5ppm, not absolute zero.