of a tank can change for a few reasons,
a. if evaporated water isn't replaced often enough. as the water evaps away the salt is too heavy to go along with the water, and it just stays in the tank, less water with the same amount of salt = higher SG
lvls, top off the tank with fresh water, and don't use salt for a top off.
b. you added to much salt, when doing a water change. following the directions of the salt company is usually a good idea, but a few times i have had tweak the mix, just to get it right
c. when water is at certain temps sg
can raise and fall based on that. if you tested in the morning when the temp was 77degrees, and retest later in the day when the tank was at 80 degrees there would be a change, somewhere about .0006 ppm
d. what hydrometer are you using? the one that floats on the top of the tank, (like they used to use on car batteries) or the one that has to filled and has a floating needle?
if your using the filled w/ needle design it is possible that air bubbles or deposits are interfering with your measurements it is always important to take care of measuring equipment, you need to rinse it with fresh water before and after each use, and once a month, soak it in a mild vinegar bath to remove deposits 30mins should be fine. Also during use make sure they are no air bubbles attached to the needle, those can through off your SG
3) When you have a pH swing upwards, its a result of CO2
absorption by algal photosynthesis. it would be a good idea to harvest the algae from the tank, or increase circulation. an easy way to test if CO2
is to blame, take a cup or two from the tank, and test its ph
, then aerate the water for a couple of hrs, and re check, if the pH has increased by a point or two, then your system is accumulating co2
and you need to increase circulation (to aid in oxygenation) or adding an air stone or two. but still 8.3 - 8.4 in my book is a' ok.
4) ammonia can be created by rotting plants, fish, food, overstocked aquarium and being routinely generated by the fish themselves. if the tank was successfully cycled, then you are probably overfeeding, or have the tank over stocked. Given the list in your signature. i feel youâ€™re a little to close to being overstocked, hermits and snails don't generate as much ammo. as fish, they still generate some. There could also be some dissolved organics in the tank that are allowing the ammo. To raise, are you running a protein skimmer?