Hi John,
795 TDS is quite high, especially given that your tap water is only 350. Im guessing that your tank tds after a water change is still quite high as 30% water change with 350 tds wont drop the tank tds a huge amount, maybe around 100tds maximum? I dont think there is anything in the tank that could be effecting TDS to that degree so my guess would be a gradual build up over time, with the 30% weekly water changes not being enough to dilute it.
Personally id be aiming to keep the tds sub 450, so to implement the change i would increase your water changes to at least 2x per week, or more smaller ones as suggested above until the level is reached.....your tap water is fine so id maybe try to get the tds lower than 450, say 350-400 and then weekly 30% water changes should keep it stable without too much change over the course of a week. If you see it rising, perform extra water changes to keep it stable and look at reducing fert dosing (you may also need to lower lighting intensity).
C02 addition makes the tank high tech, so with that and fert dosing extra organic waste is produced by the plants which needs to be cleaned. Your filter removes some, but water changes the most part. Regular filter cleaning is important to prevent build up and breakdown of detrius which can add to the organic load and increase bod.
I dont know what/how often you are feeding the livestock, but im guessing to feed the ottos its a daily routine. When you start adding food daily and shrimp are feeding daily its surprising how much waste the tank produces. This combined with the by products of a high tech tank Id begin also cleaning your filter sponge as part of a weekly maintenance routine, and rinse the noodles monthly.
Keeping the tank clean is key, i have probably 200+ CRS in my 55l nano tank, fed daily (due to the numbers) and manage to keep tds stable at sub 180. I use liquid carbon and tropica fertiliser daily. I perform weekly 30% water changes and clean the filter floss and sponge at every water change....they are filthy every time! I know from my experiences with this tank that keeping the tank clean is the key to success. Drop filter maintenance or water changes and the shrimp stop breeding
Stick with it mate, its just a case of a couple of alterations and youll have them breeding again in no time.
Cheerio,
Ady.