We have had our tank for a while now, and the tank was fully cycled at one point, it certainly tested as being fully cycled.
I did a water test today (was last changed 6 days ago), and the readings are Ammonia: 0 ppm, Nitrite 0 ppm and Nitrate 0 ppm.
This is making NO sense to me at all. The pH test works properly (granted it shows a pH of 6, but I am correcting that).
Our water pH is 7, so why on earth is the water going from 7 to 6 over time? Also, any reason why all the reading appear to be 0. I am at a loss. I want to fix all this before my girlfriend (Aza) gets back, as I am looking after the fish for her until 25th August. Also, a new tank is in the works for September, so until then, I just need to keep them going in the small tank :( Any help you be great! Also, can anyone recommend some good plants for the tank, and where to buy them? Thanks
Which test kit are you using - I'll assume API for now?
0 nitrte is unusual, what is the nitrate reading for your tap water?
Also, the nitrate test is the easiest to mess up as directions have to be followed exactly and timings need to be precise. Make sure you shake bottle no2 very vigorously for 30 seconds before adding drops to test tube and then shake tube very vigorously for a full minute before setting aside for 5 minutes and then reading the results.
pH dropping over time is common and is the result of the bacterial processing of waste, which also acidifies the water. This lowers kH which in turn causes pH to fall, and is especially noticeable if your tap kH is low to start with. Do you know what the kH of your tap water is?
One other thing to check is that test kits aren't out of date. The first to go off is the nitrate test, though it should be good for up to 3 years after production. You can tell when the tests were manufactured by looking at the lot number on the bottles - the last four digits represent the month and year of manufacture.
kH is carbonate hardness, or temporary hardness, and is related to gH or general hardness. kH is also known as alkalinity and the degree of alkalinity in the water affects the level of pH and its ability to resist changes due to acidification.
If you have soft water (low gH) you probably also have low alkalinity (low kH) and that will be the reason for your pH falling quite quickly. You may need to buffer the water slightly with crushed coral in the filter. Best to get hold of a kH/gH test kit (about ?7 on eBay) and find out what levels you have.
With your nitrate test, try banging the bottle a few times on a table before yo do all the shaking. The contents of the bottle can get stuck and not mix properly and if this happens then the reading will be wrong.
Have you used any medication recently that could have affected the bacteria?
Yes, it will slowly dissolve raising alkalinity (kH) which should prevent your pH from falling so rapidly. You won't need much, maybe a tablespoonful or so in a popsock inside the filter. After a month or two it will be less effective and need replacing. You can tell when this is needed as kH will begin to drop.