Is Zakat obligatory on capital invested in investment funds if its loss reaches 70%, with no steady income for the investor who supports a family and has significant financial obligations?

Zakat is obligatory on shares if they reach the nisab (minimum threshold) and a hawl (one lunar year) passes over them. Whatever is spent from them does not waive the zakat on the remainder, if it does not fall below the nisab. Debts are deducted from the value of the shares when zakat becomes due. If no nisab remains, zakat is waived; otherwise, zakat is paid on the remaining amount.