Diatoms Issue With High Tds

Hi all, i'm a new user and so excited to be here. I've been following and lurking around here for quite a while, but somehow I managed to live off your wisdom without ever contributing or needing much help... Well, that day has come.

Last year I moved to an old 100 year old house that runs off even older piping and infrastructure. I don't have a TDS meter, but I see calcium deposits in the bathtubs, sinks and pretty much everywhere, so I'm thinking that this is the cause of my 3 month tank having had a 2 month battle of diatoms. It was cycled after the first month. I tried about everything I could think of at the time, from dropping lights ferts and blackouts, to crazy amounts of water changes but it didn't give up at all. I had to do 3 90%+ water changes a week to keep my AR clean but vaccuming brought hell on my carpeting plants, so they eventually became unhealthy and contributed to the mess, until I was forced to reset over the weekend. The 40g tank was dirted with platinum soil cap, had co2 at a 1ph drop, with 80% plant coverage and dosed at 80% of EI. Most of them were slow growers. Buce, anubias, blood vomit, pinnatifida, AR mini, hc cuba etc. ~80% power on Chihiros RGB Vivid starting from 7, down to 4 hours a day.

My plants and filter are now on a new tank while my old one is being gutted and bleached, but the situation was quite dire and I'm hesitant to put them back in even after a bleach dip. So with all of the above being said, my question is: Does anyone have any advice so I can be sure this won't happen again? Should I increase photo period and intensity right off the bat in order to out compete diatoms with another, less aggressive type of algae? I have some phosguard and purigen, does it make sense to use this on a lower-than-before-tech environment, where i'm dosing the things the filter pads are supposed to absorb? IF it does happen again, do you recommend that I return the water to the tank after siphoning out as many diatoms as I can (thus starving diatoms of their silicates?).

I can't believe how many questions this problem has made me ask, but damn i'm looking forwards to getting some answers and finally being a part of the community.

Cheers!

 

Thanks for the reply! Ph from the tap is 7.5, in the tank it's 6.5. Got a KH test, which surprisingly came out at 3, which explains why blood vomit didn't do so badly. Don't have a softener, but I wouldn't be surprised if there was one upstream somewhere.

>>A TDS reading won't help you much because it can't distinguish between CaCO3 (i.e. KH which increases alkalinity), CaSO4 (permanent hardness, not KH, does not increase alkalinity), or sodium ions from an ion exchange water softener (is there one in the house?).

Which of these could have been the cause of stubborn diatoms? CaSO4 or Sodium?