It is critical to keep all the parameters in the tank at the correct level and more importantly to keep them stable. I manage to keep my levels quite stable due to the volume of water in the tank. The bigger the tank the more stable it will be. The chart below shows the levels that I try to maintain, occasionally you will get a glitch but generally speaking this is where it stays.

How the levels are kept stable:
There are over a douzen different parameters that need keeping stable and balancing them all is a fine art some may say. It is not as straight forward as some may think to keep the levels all ok. For example, if you just increase the calcium on its own, the kH goes down. I have trid to explain as best as possible how I manage to balance it all.

Water Temperature:
To maintain apparoximately 27oC constantly in the tank I use two 200w heaters connected directly to my IKS controller which monitors the temperature with a submerged probe. The tank will settle at 26oC during the night and when the lights come on at lunch time the water temperature slowly rises to 28oC at the most over 8 hours and then starts to drop again. Once the lights come on at 12pm the heaters do not come on again until 12am to 1am when the water drops down to the minimum temperature. I have one heater that comes on first, the other one is there as a fail safe incase the first one fails to come on. Should the tank get too hot, I will turn the main halide lights off.

Air Temperature:
The air temperature is not a critical parameter to keep monitored, but I do as I have a spare probe. During the day the air temperature 1" above the water is gererally 2 oC hotter than the water. If the air temperature was to get very hot, it would reduce the amount on oxygen in the air and there is a small chance the air being drawn into the protein skimmer wont have the same effect on the water that it does. Also hot stuffy air is not good to have around the tank, a fresh air breeza is ideal. A breeze is created with two 6" fans at either end of the tank blowing the hot air away. I also have airconditioning in the room to maintain a stable temperature thats ok for the fish.

Specific Gravity:
The Specific Gravity of the tank or Salt level as itsalso know is the easiest level to keep stable. Salt does not go anywhere and does not evaporate so the level cannot change. So long as I mix 900g of Salt to 25 Litres of water when I do a water change the salt will stay at 1.024 constantly unless I do a water change and do not replace the same amount of salt taken out.

Phosphate:
The Phosphate in the tank stays almost at 0 just doing water changes but this is not always enough so I have an adsorbent media to help it stay low. I use 1 Litre of RowaPhos in a Deltec FR509 Reactor and have found it to be very effective. Before I started using RowaPhos I have masses of long hairy algae which I was struggling to get rid of but now I dont have any at all. So to stabalise the Phosphates I use Rowa Phos and would highly recommend it.

Calcium:
I manage to maintain my Calcium level at 400 - 450ppm by doing regular 15% (60 Litres) water changes every week. The calcium is replaced from the water. I was also adding suppliments into the water such as Tropic marin Bio-Calcium to keep it at the correct level. Corals use calcium up especially hard corals for their skeletal like structure. The best answer to keep your calcium at a stable level of 450ppm is to invest in a Calcium Reactor and CO2 Set but this can be quiet a costly setup. You have to think do I keep buying suppliments which are not particularly cheap or buy a calcium reactor setup which will save money in the long run. I have a Deltec Calcium Reactor and CO2 set as I plan on keeping my reef system for some years.

pH:
To keep the pH at approximately 8.3 I have a good air flow over the tank and lots of surface movment on the water so that the water and air mix. Fresh air into the Protein skimmer can also help to keep the pH stable. Freshly mixed RO water and Salt should come out at 8.2 - 8.3 pH, when I mix my fresh RO and Salt i leave an airpump blowing air through it for 12 - 24 hours before I put it in the tank. Blowing air through the water raises the pH. If the Calcium and kH levels are too low the pH will be low so its important to make sure the other levels are where they should be. The pH is really the least important level to worry about as most marine inhabitants will be ok between 7.5 and 9.0 pH. Corals and the Majority of fish would rather be kept in a pH of 8.0 - 8.5. Sudden changes to the pH can have bad affects on the inhabitants of the tank so its important to keep it stable and not fluctuating too much. It will drop slightly in the night, maybe from 8.2 to 8.0 pH.

kH & dKH:
The kH and dKH is the water hardness, this is directly linked to the Calcium level. If you increase on the other goes down so it is critical to keep both stable as it will affect the kH, the calcium and indirectly affect the pH. The dKH is the same as kH but you divide it by 18.9 to get the dkH. I aim to keep the tank at 225ppm kH which is the same as 11.0 dkH. Water hardness is maintained by just doing water changes each week. This generally keeps the level correct, but supposing the tank gets a calcium deficiency the kH will increase so its important to see that the Calcium stays stable at 400 - 450ppm. To maintain the kH at this level I use Kent suppliments to stabilise that and the calcium, its increases them at the same rate cancelling the rise out making it stable basically. The kH is tested with a test tube and drops of kH testing solution. I have no way of digitally testing this parameter.

Nitrate:
The Nitrate in my tank is kept under control by a huge amount of culurpa that i have in the sump and a 4" deep sand bed and a good load of Miracle Mud. The rest of the system tends to look after iteself. The main thing that strips the Nitrate is the Culurpa and the DSB. However you cant beat a good water change. Nitrate is a bad thing generally speaking to have in your system so its best getting rid of it, if you have no nitrates its fact that things will grow better!

Redox:

Nitrite:

Ammonia:

Magnesium & Iron