Ph is dropping in my 30 gallon. Need help

55bldparrot30

i have a 30 gallon tank that has been set up for about 7 months. For months the tank stayed at 7.2( doing all the required water changes of coarse)and starting dropping as expected with an aging tank. At around 6.4 in ph i decided to add crushed coral to stabalize the ph. I added a 1/4 cup and it barely moved. I then added a 1/2 cup and it came to about 6.8. I decided that was reasonable so i left it at that and when i did my 25% water change with water of 7.2 it came up to about 6.9 and by morning it had dropt way down to 6.2-6.3. How has this happend and did i not add enough crushed coral.A couple days later so not to stress the fish. I have added another 1/2 cup \ and history has repeated exactly how i have said before.It came to 6.8 , when i did the water change it drops to 6.2-6.3. So what is happening? Do i need more crushed coral ? There is about 1 1/2 to 2 cups of coral in now.

Lupin

Strange. What test kit are you using? What are your hardness levels? Your other alternatives are marble chips, plaster of Paris blocks and limestones.

55bldparrot30

My hardness level is 75-100 ppm and the alkalinity is 40 ppm if not lower. The test kit is API ,aquarium pharmaceuticals . I dont understand. If the tank reacted to the coral how could it drop below the 6.8 it had been buffered too.

Lupin

Your hardness level is soft. What's the hardness of your tapwater? Add more crushed corals. If this does not help, go over plaster of Paris blocks or marble chips.

55bldparrot30

My tap water is hard ,but i have been using store bought water, which is soft. So i hopefully wouldnt get the big ph swing that i have been getting. Is 1 1/2 cups not enough. Someone told me that was hardly enough to do anything.

55bldparrot30

do the paris block or marble chips work better than crushed coral

Lupin

Tapwater should be fine. It buffers pH easily. What is your reason for using RO water? This is a waste of time and a tedious process to begin with.

Both of the things I mentioned can last for a long time and can also help stabilized the pH. Plaster of Paris is cheap and you just make several blocks as desired and add once they dissolve quickly but from your first post, you have no reason to use RO water. Just use tapwater.

55bldparrot30

My tap water has about 20 to 25 ppm of nitrate present and i do not have a planted tank. so this is why i decided to use store bought.I am not using RO water but store bought spring water in hopes that it is not missing all its major properties.

55bldparrot30

Is this why my tank has this low ph and struggles to come up? Because of the softer store bought spring water i have been using in my tank. If so , when i use my well water, the ph in the tank rises for a couple hours then drops because of the tanks buffering capacity which i thought would be bad for the fish. What do you suggest? Mayb add corals to bring it up to about 7.0- 7.2 and then do a water change?

Lupin

Hornworts are your best bet. They do not taste well so most fish ignore them completely.