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hi my tds is 50 at the moment what should it be many thanks

There is no "should it be' per se. It depends on a few things. What will count in the longer run for spawning is the change in tds. I have seen numbers from the wild taken from the Xingu near Altamira (the top of the big bend) that were a low of about 14 ppm and a pH of low 6s to 85 ppm anh high 6s/low 7s. These were take a few years apart one during the dry and the other during the rainy season. This indicates a tds change of about 60-70 ppm seem to be sufficient to trigger them.

At best consider raising your tds to the 110-120 range so your tap at 50 would be that much of a difference.

But it would also be possible to have 150ish ppm as dry and 80ish ppm as rainy as far as I can tell.

ps- Welcome to the site

many thanks for the post holly

My TDS is normally about 135. When I do a water change I try to get close...say between 110 and 135.

I am not sure if it is the decrease and TDS or the decrease of nitrates in the water (or a combination of the two) which helps trigger a spawn.

How could it be the nitrates since these are not a factor in the wild at all?

I could be the TDS, it could be the temp, it could be the current, it could be the food supply, it could be the barometric pressure. Any and all of these change in the wild but there are no issues regarding cycling in the wild.

My theory is that the decrease in dissolved organics helps trigger a spawn in captive bred zebras. It's a theory, and would be difficult to prove, but it is a theory. The reason that I think the theory might be valid is that during water changes I don't noticeably alter the TDS or temperature, yet my zebras tend to spawn after a large water change.