I have three freshwater tanks, 40, 150, 1800 (eighteen hundred) gallons.

My tap water is over 8.0 All my tanks and the tap water have KH of LESS than 15 ppm (one drop in API test). Over time the ph in all tanks has dropped to the 6-6.4 range, and I'd like to keep it closer to 7. When I add baking soda the ph goes up WAY faster than the KH, which hardly moves. I DO NOT have a phosphate problem, and ammonia, TRITE and TRATE are in very low acceptable levels.

How can I raise my KH to over 50ppm AND STABILIZE my ph at 6.8-7.2?

P.S. last week I raised the 1800 tank from kh<15 to around kh30, and ph went from 6.0 to 6.3. However, the kh has gone back down to <15.

I'm pretty experienced and have never seen this problem before.

Can anybody help?

Thanks

Hmmm...I don't think that you can effectively raise one parameter without impacting the others. KH/GH and pH are all tied in together.

I'm curious to know more about your setups. You say you're pH is 8 from the tap and then drops to mid 6? As per your description (good one by the way), your water has no buffering abilities to maintain the levels. Baking Soda is kind of a short action fix.

You don't by change inject CO2 do you?

If you're looking to stabilize it, I would suggest using Crushed Coral. This will raise your pH as well as increase the waters buffering abilities. In turn, your GH/KH values will increase as well.

Thanks for your reply. I don't use CO2, as there are no plants, and that would just lower the ph further anyway.

Somebody who "SHOULD" know told me I could use cured Plaster of Paris pancakes instead of crushed coral, as it is way less expensive on the scale I would need it. Do you know about this?

My tank is about 11x15x2 (feet) and is outdoors. I am going to enlarge it to 15x12x3.25 soon. It has eleven koi from 12 to 36 inches (mostly around 14-24), about 50+/- cichlids and a few assorted larger tropicals. I also have some rope fish and bichers to eat the babies or I would have no water, just fish, after a while.

Thanks

Unfortunately I can't comment on the PoP. I've never used it. I've of people using for inverts however.

If you don't mind me asking...I would love to see the outdoor tank. I'm looking to start on a deck pond myself soon which will be rather large.