A couple of my smaller ponds (less than 100L) are going basic, normally their PH is between 6.4-6.8, but in the past 2weeks a few are 7.2-7.6 and 1 got to 8.2.
To counter it I use spag, I throw a handful in and for a couple days the PH drops to 6.6-7.0, Most of them have CO2 generators and a peat or spag bottom.
I have never had this issue before, at first I thought it was the neigbours cat, as I have seen it urinate in the ponds, but I set up a few test tanks (4cm layer of spag in 2, 5cm peat layer in the other two then a 3cm sand layer) for the first week they are 6.4-6.8, but after a week they spike to 7.2-7.6.
Another odd thing is that my ponds in my polyhouse and a tank with a lid that coveres half the tanks top (mostly to keep rain from filling it) are holding a good PH range (6.4-6.6).
I am leaning towards either some form of animal has got in (as I have a new type of snail that has sprung up in my collection) or maybe an airborn substance, unless bacteria can do this?
So far it is confined to my collection I keep with me at uni and not at the bulk of my collection at dads (1-2hours north), and I have put a halt to moving any of my aquatics between the two.
On a side note many of my U.Aurea in these ponds are making red traps, I have a couple aurea varieties that go red anyway, but they normally have red stems and branches to go with the traps, perhaps this is a hint.